Ocean Thermal Energy Conversion Power Plant

ABSTRACT

An offshore power generation structure comprising a submerged portion having a first deck portion comprising an integral multi-stage evaporator system, a second deck portion comprising an integral multi-stage condensing system, a third deck portion housing power generation equipment, cold water pipe; and a cold water pipe connection.

TECHNICAL FIELD

This disclosure relates to ocean thermal energy conversion power plantsand more specifically to floating, minimum heave platform, multi-stageheat engine, ocean thermal energy conversion power plants.

BACKGROUND

Energy consumption and demand throughout the world has grown at anexponential rate. This demand is expected to continue to rise,particularly in developing countries in Asia and Latin America. At thesame time, traditional sources of energy, namely fossil fuels, are beingdepleted at an accelerating rate and the cost of exploiting fossil fuelscontinues to rise. Environmental and regulatory concerns areexacerbating that problem.

Solar-related renewable energy is one alternative energy source that mayprovide a portion of the solution to the growing demand for energy.Solar-related renewable energy is appealing because, unlike fossilfuels, uranium, or even thermal “green” energy, there are few or noclimatic risks associated with its use. In addition, solar relatedenergy is free and vastly abundant.

Ocean Thermal Energy Conversion (“OTEC”) is a manner of producingrenewable energy using solar energy stored as heat in the oceans'tropical regions. Tropical oceans and seas around the world offer aunique renewable energy resource. In many tropical areas (betweenapproximately 20° north and 20° south latitude), the temperature of thesurface sea water remains nearly constant. To depths of approximately100 ft the average surface temperature of the sea water variesseasonally between 75° and 85° F. or more. In the same regions, deepocean water (between 2500 ft and 4200 ft or more) remains a fairlyconstant 40° F. Thus, the tropical ocean structure offers a large warmwater reservoir at the surface and a large cold water reservoir atdepth, with a temperature difference between the warm and coldreservoirs of between 35° to 45° F. This temperature difference remainsfairly constant throughout the day and night, with small seasonalchanges.

The OTEC process uses the temperature difference between surface anddeep sea tropical waters to drive a heat engine to produce electricalenergy. OTEC power generation was identified in the late 1970's as apossible renewable energy source having a low to zero carbon footprintfor the energy produced. An OTEC power plant, however, has a lowthermodynamic efficiency compared to more traditional, high pressure,high temperature power generation plants. For example, using the averageocean surface temperatures between 80° and 85° F. and a constant deepwater temperature of 40° F., the maximum ideal Carnot efficiency of anOTEC power plant will be 7.5 to 8%. In practical operation, the grosspower efficiency of an OTEC power system has been estimated to be abouthalf the Carnot limit, or approximately 3.5 to 4.0%. Additionally,analysis performed by leading investigators in the 1970's and 1980's,and documented in “Renewable Energy from the Ocean, a Guide to OTEC”William Avery and Chih Wu, Oxford University Press, 1994 (incorporatedherein by reference), indicates that between one quarter to one half (ormore) of the gross electrical power generated by an OTEC plant operatingwith a ΔT of 40° F. would be required to run the water and working fluidpumps and to supply power to other auxiliary needs of the plant. On thisbasis, the low overall net efficiency of an OTEC power plant convertingthe thermal energy stored in the ocean surface waters to net electricenergy has not been a commercially viable energy production option.

An additional factor resulting in further reductions in overallthermodynamic efficiency is the loss associated with providing necessarycontrols on the turbine for precise frequency regulation. Thisintroduces pressure losses in the turbine cycle that limit the work thatcan be extracted from the warm sea water.

This low OTEC net efficiency compared with efficiencies typical of heatengines that operate at high temperatures and pressures has led to thewidely held assumption by energy planners that OTEC power is too costlyto compete with more traditional methods of power production.

Indeed, the parasitic electrical power requirements are particularlyimportant in an OTEC power plant because of the relatively smalltemperature difference between the hot and cold water. To achievemaximum heat transfer between the warm sea water and the working fluid,and between the cold sea water and the working fluid large heat exchangesurface areas are required, along with high fluid velocities. Increasingany one of these factors can significantly increase the parasitic loadon the OTEC plant, thereby decreasing net efficiency. An efficient heattransfer system that maximizes the energy transfer in the limitedtemperature differential between the sea water and the working fluidwould increase the commercial viability of an OTEC power plant.

In addition to the relatively low efficiencies with seemingly inherentlarge parasitic loads, the operating environment of OTEC plants presentsdesign and operating challenges that also decrease the commercialviability of such operations. As previously mentioned, the warm waterneeded for the OTEC heat engine is found at the surface of the ocean, toa depth of 100 ft or less. The constant source of cold water for coolingthe OTEC engine is found at a depth of between 2700 ft and 4200 ft ormore. Such depths are not typically found in close proximity topopulation centers or even land masses. An offshore power plant isrequired.

Whether the plant is floating or fixed to an underwater feature, a longcold water intake pipe of 2000 ft or longer is required. Moreover,because of the large volume of water required in commercially viableOTEC operations, the cold water intake pipe requires a large diameter(typically between 6 and 35 feet or more). Suspending a large diameterpipe from an offshore structure presents stability, connection andconstruction challenges which have previously driven OTEC costs beyondcommercial viability.

Additionally, a pipe having significant length to diameter ratio that issuspended in a dynamic ocean environment can be subjected to temperaturedifferences and varying ocean currents along the length of the pipe.Stresses from bending and vortex shedding along the pipe also presentchallenges. Surface influences such as wave action present furtherchallenges with the connection between the pipe and floating platform. Acold water pipe intake system having desirable performance, connection,and construction consideration would increase the commercial viabilityof an OTEC power plant.

Environmental concerns associated with an OTEC plant have also been animpediment to OTEC operations. Traditional OTEC systems draw in largevolumes of nutrient rich cold water from the ocean depths and dischargethis water at or near the surface. Such discharge can effect, in apositive or adverse manner, the ocean environment near the OTEC plant,impacting fish stocks and reef systems that may be down current from theOTEC discharge.

SUMMARY

Aspects of the present disclosure are directed to a power generationplant utilizing ocean thermal energy conversion processes.

An offshore OTEC power plant has improved overall efficiencies withreduced parasitic loads, greater stability, lower construction andoperating costs, and improved environmental footprint. Other aspectsinclude large volume water conduits that are integral with the floatingstructure. Modularity and compartmentation of the multi-stage OTEC heatengine reduces construction and maintenance costs, limits off-gridoperation and improves operating performance. Still further aspectsprovide for a floating platform having integrated heat exchangecompartments and provides for minimal movement of the platform due towave action. The integrated floating platform may also provide forefficient flow of the warm water or cool water through the multi-stageheat exchanger, increasing efficiency and reducing the parasitic powerdemand. Aspects of the systems and methods described can promote anenvironmentally neutral thermal footprint by discharging warm and coldwater at appropriate depth/temperature ranges. Energy extracted in theform of electricity reduces the bulk temperature to the ocean.

Still further aspects of the systems and methods described relate to acold water pipe for use with an offshore OTEC facility, the cold waterpipe being an offset staved, continuous pipe.

One aspect relates to a pipe that comprises an elongate tubularstructure having an outer surface, a top end and a bottom end. Thetubular structure comprises a plurality of first and second stavedsegments, each stave segment has a top portion and a bottom portion,wherein the top portion of the second stave segment is offset from thetop portion of the first staved segment.

A further aspect relates to a pipe comprising a ribbon or a strake atleast partially wound around the pipe on the outside surface of thetubular structure. The ribbon or strake can be circumferentially woundaround the outer surface of the top portion of the pipe, the middleportion of the pipe, or the lower portion of the pipe. The ribbon orstrake can be circumferentially wound around the entire length of thepipe. The ribbon or strake can be attached so as to lay substantiallyflat against the outer surface of the pipe. The ribbon or strake can beattached so as to protrude outwardly from the outer surface of the pipe.The ribbon or strake can be made of the same or different material asthe pipe. The ribbon or strake can be adhesively bonded to the outersurface of the pipe, mechanically bounded to the outer surface of thepipe, or use a combination of mechanical and adhesive bonds to attach tothe outer surface of the pipe.

Further aspects of the systems and methods described relate to an offsetstaved pipe wherein each stave segment further comprises a tongue on afirst side and a groove on a second side for mating engagement with anadjacent stave segment. The offset stave pipe can include a positivelocking system to mechanical couple a first side of one stave to thesecond side of a second stave. Staves can be joined vertically from thetop portion of one stave to the bottom portion of an adjacent staveusing biscuit joinery. In an alternative embodiment, the top portion ofa stave and the bottom portion of a stave can each include a joiningvoid, such that when the top portion of a first stave is joined with thebottom portion of a second stave, the joining voids align. A flexibleresin can be injected into the aligned joining voids. The flexible resincan be used to fill gaps in any joined surfaces. In aspects of thesystems and methods described the flexible resin is a methacrylateadhesive.

Individual staves of the current systems and methods described can be ofany length. In some embodiments, each stave segment is between 20 feetand 90 feet measured from the bottom portion to the top portion of thestave. Stave segments can be sized to be shipped by standard inter-modalcontainer. Individual stave segments can be between 10 inches and 80inches wide. Each stave segment can be between 1 inch and 24 inchesthick.

Stave segments can be pulltruded, extruded, or molded. Stave segmentscan comprise polyvinyl chloride (PVC), chlorinated polyvinyl chloride(CPVC), fiber reinforced plastic (FRP), reinforced polymer mortar(RPMP), polypropylene (PP), polyethylene (PE), cross-linked high-densitypolyethylene (PEX), polybutylene (PB), acrylonitrile butadiene styrene(ABS); polyester, fiber reinforced polyester, vinyl ester, reinforcedvinyl ester, concrete, ceramic, or a composite of one or more thereof.

In further aspects of the systems and methods described, a stave segmentcan comprise at least one internal void. Then at least one void can befilled with water, polycarbonate foam, or syntactic foam.

In aspects of the systems and methods described, the pipe is a coldwater intake pipe for an OTEC power plant.

A still further aspect of the systems and methods described relates toan offshore power generation structure comprising a submerged portion,the submerged portion further comprises: a heat exchange portion; apower generation portion; and a cold water pipe comprising a pluralityof offset first and second stave segments.

Yet another aspect of the systems and methods described relates to amethod of forming a cold water pipe for use in an OTEC power plant, themethod comprises: forming a plurality of first and second stave segmentsjoining alternating first and second stave segments such that the secondstave segments are offset from the first stave segments to form acontinuous elongated tube.

A further aspect of the systems and methods described relates to asubmerged vertical pipe connection comprising: a floating structurehaving a vertical pipe receiving bay, wherein the receiving bay has afirst diameter; a vertical pipe for insertion into the pipe receivingbay, the vertical pipe having a second diameter smaller than the firstdiameter of the pipe receiving bay; a partially spherical or arcuatebearing surface; and one or more movable detents, pinions or lugsoperable with the bearing surface, wherein the detents define a diameterthat is different than the first or second diameter when in contact withthe bearing surface.

An additional aspect of the systems and methods described relates to amethod of connecting a submerged vertical pipe to a floating platformcomprising: a floating structure having a vertical pipe receiving bay,wherein the pipe receiving bay has a first diameter, providing avertical pipe having a top end portion that has a second diameter thatis less than the first diameter; inserting the top end portion of thevertical pipe into the receiving bay; providing a bearing surface forsupporting the vertical pipe; extending one or more detents such thatthe one or more detents have a diameter that is different from the firstor second diameters; contacting the one or more detents with the bearingsurface to suspend the vertical pipe from the floating structure.

In aspects of the systems and methods described the one or more detentscan be integral to the vertical pipe. The one or more detents can beintegral to the receiving bay. The one or more detents comprise a firstretracted position that defines a diameter less than the first diameter.The one or more detents comprise an extended position that defines adiameter greater than the first diameter. A bearing surface is integralto the pipe receiving bay and operable with the one or more detents. Thebearing surface can comprise a spherical bearing surface. The one ormore detents further comprise a mating surface configured to contact thebearing surface. The one or more detents further comprise a matingsurface configured to contact the spherical bearing surface. Thespherical bearing surface and the mating surface facilitate relativemotion between the vertical pipe and the floating structure.

In still further aspects, the one or more detents comprise a firstretracted position that defines a diameter greater than the seconddiameter. The one or more detents comprise an extended position thatdefines a diameter less than the second diameter. A bearing surface isintegral to the vertical pipe and operable with the one or more detents.

Features can include a drive for extending or retracting the detents,the drive being a hydraulically controlled drive, a pneumaticallycontrolled drive; a mechanically controlled drive, an electricallycontrolled drive, or an electro-mechanically controlled drive.

Further aspects can include a pipe receiving bay including a firstangled pipe mating surface; and a vertical pipe comprising a secondangled pipe mating surface, wherein the first and second angled pipemating surfaces are configured to cooperatively guide the vertical pipeduring insertion of the vertical pipe into the pipe receiving bay.

In still further aspects, a static interface between the cold water pipeand the lower portion of the spar is provided comprising a receiving bayhaving a tapered lower surface and a contact pad for sealable engagementwith a tapered collar surface of a cold water pipe lifting collar.

In an exemplary method of connecting a cold water pipe to a lowerportion of a spar, the method provides the steps comprising: connectinglifting and retention cables to an upper portion of a cold water pipe,wherein the cold water pipe upper portion comprises a lifting collarhaving a tapered connecting surface, drawing the cold water pipe into aspar receiving bay using the lifting and retention cables, wherein thereceiving bay comprises a tapered surface for receiving the cold waterpipe upper portion and a contact pad; causing the tapered connectingsurface of the cold water pipe to make a sealable contact with thecontact pad of the receiving bay, and mechanically fixing the liftingcables to maintain the sealable contact between the connecting surfaceand the contact pad.

In yet a further aspect, a cold water pipe is provided for staticconnection to the lower portion of a spar, wherein the cold water pipecomprises a first longitudinal portion and a second longitudinalportion; the first longitudinal portion being connected to the lowerportion of the spar and the second longitudinal portion being moreflexible than the first longitudinal portion. In some aspect a thirdlongitudinal portion can be included in the cold water pipe that is lessflexible than the second longitudinal portion. The third longitudinalportion can be more flexible then the first longitudinal portion. Thethird longitudinal portion can comprise 50% or more of the length of thecold water pipe. The first longitudinal portion can comprise 10% or lessof the length of the cold water pipe. The second longitudinal portioncan comprise between 1% and 30% of the length of the cold water pipe.The second longitudinal portion can allow for deflection of the thirdlongitudinal portion of the cold water pipe of between 0.5 degrees and30 degrees.

Further aspects of the systems and methods described relate to afloating, minimal heave OTEC power plant having an optimized multi-stageheat exchange system, wherein the warm and cold water supply conduitsand heat exchanger cabinets are structurally integrated into thefloating platform or structure of the power plant.

Still further aspects include a floating ocean thermal energy conversionpower plant. A minimal heave structure, such as a spar, or modifiedsemi-submersible offshore structure may comprise a first deck portionhaving structurally integral warm sea water passages, multi-stage heatexchange surfaces, and working fluid passages, wherein the first deckportion provides for the evaporation of the working fluid. A second deckportion is also provided having structurally integral cold sea waterpassages, multi-stage heat exchange surfaces, and working fluidpassages, wherein the second deck portion provides a condensing systemfor condensing the working fluid from a vapor to a liquid. The first andsecond deck working fluid passages are in communication with a thirddeck portion comprising one or more vapor turbine driven electricgenerators for power generation.

In one aspect, an offshore power generation structure is providedcomprising a submerged portion. The submerged portion further comprisesa first deck portion comprising an integral multi-stage evaporatorsystem, a second deck portion comprising an integral multi-stagecondensing system; a third deck portion housing power generation andtransformation equipment; a cold water pipe and a cold water pipeconnection.

In a further aspect, the first deck portion further comprises a firststage warm water structural passage forming a high volume warm waterconduit. The first deck portion also comprises a first stage workingfluid passage arranged in cooperation with the first stage warm waterstructural passage to warm a working fluid to a vapor. The first deckportion also comprises a first stage warm water discharge directlycoupled to a second stage warm water structural passage. The secondstage warm water structural passage forms a high volume warm waterconduit and comprises a second stage warm water intake coupled to thefirst stage warm water discharge. The arrangement of the first stagewarm water discharge to the second stage warm water intake providesminimal pressure loss in the warm water flow between the first andsecond stage. The first deck portion also comprises a second stageworking fluid passage arranged in cooperation with the second stage warmwater structural passage to warm the working fluid to a vapor. The firstdeck portion also comprises a second stage warm water discharge.

In a further aspect, the submerged portion further comprises a seconddeck portion comprising a first stage cold water structural passageforming a high volume cold water conduit. The first stage cold waterpassage further comprises a first stage cold water intake. The seconddeck portion also comprises a first stage working fluid passage incommunication with the first stage working fluid passage of the firstdeck portion. The first stage working fluid passage of the second deckportion in cooperation with the first stage cold water structuralpassage cools the working fluid to a liquid. The second deck portionalso comprises a first stage cold water discharge directly coupled to asecond stage cold water structural passage forming a high volume coldwater conduit. The second stage cold water structural passage comprisesa second stage cold water intake. The first stage cold water dischargeand the second stage cold water intake are arranged to provide minimalpressure loss in the cold water flow from the first stage cold waterdischarge to the second stage cold water intake. The second deck portionalso comprises a second stage working fluid passage in communicationwith the second stage working fluid passage of the first deck portion.The second stage working fluid passage in cooperation with the secondstage cold water structural passage cool the working fluid within thesecond stage working fluid passage to a liquid. The second deck portionalso comprises a second stage cold water discharge.

In a further aspect, the third deck portion may comprise a first andsecond vapor turbine, wherein the first stage working fluid passage ofthe first deck portion is in communication with the first turbine andthe second stage working fluid passage of the first deck portion is incommunication with the second turbine. The first and second turbine canbe coupled to one or more electric generators.

In still further aspects, an offshore power generation structure isprovided comprising a submerged portion, the submerged portion furthercomprises a four stage evaporator portion, a four stage condenserportion, a four stage power generation portion, a cold water pipeconnection, and a cold water pipe.

In one aspect the four stage evaporator portion comprises a warm waterconduit including, a first stage heat exchange surface, a second stageheat exchange surface, a third stage heat exchange surface, and fourthstage heat exchange surface. The warm water conduit comprises a verticalstructural member of the submerged portion. The first, second, third andfourth heat exchange surfaces are in cooperation with first, second,third and fourth stage portions of a working fluid conduit, wherein aworking fluid flowing through the working fluid conduit is heated to avapor at each of the first, second, third, and fourth stage portions.

In one aspect the four stage condenser portion comprises a cold waterconduit including, a first stage heat exchange surface, a second stageheat exchange surface, a third stage heat exchange surface, and fourthstage heat exchange surface. The cold water conduit comprises a verticalstructural member of the submerged portion. The first, second, third andfourth heat exchange surfaces are in cooperation with first, second,third and fourth stage portions of a working fluid conduit, wherein aworking fluid flowing through the working fluid conduit is heated to avapor at each of the first, second, third, and fourth stage portions,with lower a lower ΔT at each successive stage.

In yet another aspect, first, second, third and fourth stage workingfluid conduits of the evaporator portion are in communication with afirst, second, third and fourth vapor turbine, wherein the evaporatorportion first stage working fluid conduit is in communication with afirst vapor turbine and exhausts to the fourth stage working fluidconduit of the condenser portion.

In yet another aspect, first, second, third and fourth stage workingfluid conduits of the evaporator portion are in communication with afirst, second, third and fourth vapor turbine, wherein the evaporatorportion second stage working fluid conduit is in communication with asecond vapor turbine and exhausts to the third stage working fluidconduit of the condenser portion.

In yet another aspect, first, second, third and fourth stage workingfluid conduits of the evaporator portion are in communication with afirst, second, third and fourth vapor turbine, wherein the evaporatorportion third stage working fluid conduit is in communication with athird vapor turbine and exhausts to the second stage working fluidconduit of the condenser portion.

In yet another aspect, first, second, third and fourth stage workingfluid conduits of the evaporator portion are in communication with afirst, second, third and fourth vapor turbine, wherein the evaporatorportion fourth stage working fluid conduit is in communication with afourth vapor turbine and exhausts to the first stage working fluidconduit of the condenser portion.

In still a further aspect, a first electrical generator is driven by thefirst turbine, the fourth turbine, or a combination of the first andfourth turbine.

In still a further aspect, a second electrical generator is driven bythe second turbine, the third turbine, or a combination of both thesecond and third turbine.

Additional aspects of the systems and methods described can incorporateone or more of the following features: the first and fourth turbines orthe second and third turbines produce between 9 MW and 60 MW ofelectrical power; the first and second turbines produce approximately 55MW of electrical power; the first and second turbines form one of aplurality of turbine-generator sets in an Ocean Thermal EnergyConversion power plant; the first stage warm water intake is free ofinterference from the second stage cold water discharge; the first stagecold water intake is free of interference from the second stage warmwater discharge; the working fluid within the first or second stageworking fluid passages comprises a commercial refrigerant. The workingfluid comprises ammonia, propylene, butane, R-134, or R-22; the workingfluid in the first and second stage working fluid passages increases intemperature between 12° F. and 24° F.; a first working fluid flowsthrough the first stage working fluid passage and a second working fluidflows through the second stage working fluid passage, wherein the secondworking fluid enters the second vapor turbine at a lower temperaturethan the first working fluid enters the first vapor turbine; the workingfluid in the first and second stage working fluid passages decreases intemperature between 12° F. and 24° F.; a first working fluid flowsthrough the first stage working fluid passage and a second working fluidflows through the second stage working fluid passage, wherein the secondworking fluid enters the second deck portion at a lower temperature thanthe first working fluid enters the second deck portion.

Further aspects of the systems and methods described can alsoincorporate one or more of the following features: the warm waterflowing within the first or second stage warm water structural passagecomprises: warm sea water, geo-thermally heated water, solar heatedreservoir water; heated industrial cooling water, or a combinationthereof; the warm water flows between 500,000 and 6,000,000 gpm; thewarm water flows at 5,440,000 gpm; the warm water flows between300,000,000 lb/hr and 1,000,000,000 lb/hr; the warm water flows at2,720,000 lb/hr; the cold water flowing within the first or second stagecold water structural passage comprises: cold sea water, cold freshwater, cold subterranean water or a combination thereof; the cold waterflows between 250,000 and 3,000,000 gpm; the cold water flows at3,420,000 gpm; the cold water flows between 125,000,000 lb/hr and1,750,000,000 lb/hr; the cold water flows at 1,710,000 lb/hr.

Aspects of the systems and methods described can also incorporate one ormore of the following features: the offshore structure is a minimalheave structure; the offshore structure is a floating spar structure;the offshore structure is a semi-submersible structure.

A still further aspect of the systems and methods described can includea high-volume, low-velocity heat exchange system for use in an oceanthermal energy conversion power plant, comprising: a first stage cabinetthat further comprises a first water flow passage for heat exchange witha working fluid; and a first working fluid passage; and a second stagecabinet coupled to the first stage cabinet, that further comprises asecond water flow passage for heat exchange with a working fluid andcoupled to the first water flow passage in a manner to minimize pressuredrop of water flowing from the first water flow passage to the secondwater flow passage; and a second working fluid passage. The first andsecond stage cabinets comprise structural members of the power plant.

In another aspect, water flows from the first stage cabinet to thesecond stage cabinet and the second stage cabinet is beneath the firststage cabinet evaporator. In another aspect, water flows from the firststage cabinet to the second stage cabinet and the second stage cabinetis above the first stage cabinet in the condensers and below the firststage cabinet in the evaporators.

In another aspect, a method of connecting submerged vertical pipe to afloating structure includes connecting lifting and retention cables toan upper portion of a cold water pipe, wherein the cold water pipe upperportion comprises a lifting collar having a tapered connecting surface,drawing the cold water pipe into a spar receiving bay using the liftingand retention cables, wherein the receiving bay comprises a taperedsurface for receiving the cold water pipe upper portion and a contactpad; causing the tapered connecting surface of cold water pipe to make asealable contact with the contact pad of the receiving bay; andmechanically fixing the lifting cables to maintain the sealable contactbetween the connecting surface and the contact pad.

In another aspect, a submerged pipe connection assembly includes aconnection structure comprising a lower portion having lifting devices,lifting cables, a first tapered connecting surface and a contact pad;and a vertical pipe that includes a first longitudinal portioncomprising a lifting collar having a second tapered connecting surfaceand lifting eyes; and a second longitudinal portion below the firstportion, wherein the second portion is more flexible than the firstportion.

The submerged pipe connection assembly may include one or more of thefollowing features: The submerged pipe connection assembly includes athird longitudinal portion below the second longitudinal portion andwherein the third portion is less flexible than the second portion. Thesecond tapered connecting surface is in contact with the contact pad ofthe first tapered connecting surface so as to form a watertight seal.The assembly is part of an OTEC system.

In another aspect, a submerged vertical pipe connection includes afloating structure having a vertical pipe receiving bay, wherein thereceiving bay has a first diameter; a vertical pipe for insertion intothe pipe receiving bay, the vertical pipe having a second diametersmaller than the first diameter of the pipe receiving bay; a bearingsurface; and one or more detents operable with the bearing surface,wherein the detents define a diameter that is different than the firstor second diameter when in contact with the bearing surface.

In another aspect, a method of connecting a submerged vertical pipe to afloating platform includes providing a floating structure having avertical pipe receiving bay, wherein the pipe receiving bay has a firstdiameter; providing a vertical pipe having a top end portion that has asecond diameter that is less than the first diameter; inserting the topend portion of the vertical pipe into the receiving bay; providing abearing surface for supporting the vertical pipe; extending one or moredetents such that the one or more detents have a diameter that isdifferent from the first or second diameters; and contacting the one ormore detents with the bearing surface to suspend the vertical pipe fromthe floating structure.

In another aspect, an offshore power generation structure includes asubmerged portion. The submerged portion includes a four stageevaporator portion integral with a warm water conduit, a four stagecondenser portion integral with a cold water conduit, a power generationportion, a cold water pipe connection, and a cold water pipe.

The offshore power generation structure includes one or more of thefollowing features: The four stage evaporator portion comprises: a warmwater conduit comprising a first stage heat exchange surface, a secondstage heat exchange surface, a third stage heat exchange surface, andfourth stage heat exchange surface in cooperation with first, second,third and fourth working fluids, wherein working heated to a vapor ateach of the first, second, third, and fourth stage heat exchangesurfaces. The warm water conduit comprises a structural member of thesubmerged portion. The first and fourth working fluids are incommunication with a first turbo generator and the second and thirdworking fluids are in communication with a second turbo generator.

In some aspects, an offshore power generation structure is provided thatincludes a submerged portion. The submerged portion includes a firstdeck portion, a second deck portion and a third deck portion. The firstdeck portion includes an integral multi-stage evaporator systemcomprising; a first warm water structural passage forming a high volumewarm water conduit; a first stage working fluid passage arranged incooperation with the first stage warm water structural passage to warm aworking fluid to a vapor; a first stage warm water discharge directlycoupled to a second stage warm water structural passage, wherein thesecond stage warm water structural passage forms a high volume warmwater conduit and comprises: a second stage warm water intake coupled tothe first stage warm water discharge; a second stage working fluidpassage arranged in cooperation with the second stage warm waterstructural passage to warm a second working fluid to a vapor; a secondstage warm water discharge. The second deck portion includes an integralmulti-stage condensing system, comprising: a first stage cold waterstructural passage forming a high volume cold water conduit, the firststage cold water passage further comprises: a first stage cold waterintake; a first stage working fluid passage in communication with thefirst stage working fluid passage of the first deck portion, wherein theworking fluid passage of the second deck portion in cooperation with thefirst stage cold water structural passage cools the working fluid to aliquid; a first stage cold water discharge directly coupled to a secondstage cold water structural passage forming a high volume cold waterconduit comprising; a second stage cold water intake wherein the firststage cold water discharge and the second stage cold water intake arearranged to provide minimal pressure loss in the cold water flow fromthe first stage cold water discharge to the second stage cold waterintake; a second stage working fluid passage in communication with thesecond stage working fluid passage of the first deck portion, whereinthe second stage working fluid passage in cooperation with the secondstage cold water structural passage cool the working fluid within thesecond stage working fluid passage to a liquid; a second stage coldwater discharge. The third deck portion houses power generationequipment, and includes a first and second vapor turbine, wherein thefirst stage working fluid passage of the first deck portion is incommunication with the first turbine and the second stage working fluidpassage of the first deck portion is in communication with the secondturbine.

In some aspects, a pipe includes an elongated tubular structure havingan outer surface, a top end and a bottom end, the tubular structurecomprising: a plurality of first and second stave segments, each stavesegment having a top portion and a bottom portion, wherein the topportion of the second stave segment is offset from the top portion ofthe first staved segment. In addition, each stave segment comprisespolyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC), fiberreinforced plastic (FRP), reinforced polymer mortar (RPMP),polypropylene (PP), polyethylene (PE), cross-linked high-densitypolyethylene (PEX), polybutylene (PB), acrylonitrile butadiene styrene(ABS); polyester, fiber reinforced polyester, nylon reinforcedpolyester, vinyl ester, fiber reinforced vinyl ester, nylon reinforcedvinyl ester, concrete, ceramic, or a composite of one or more thereof.

In some aspects, a method of forming a cold water pipe for use in anOTEC power plant includes forming a plurality of first and second stavesegments; and adhesively bonding alternating first and second stavesegments such that the second stave segments are offset from the firststave segments to form a continuous elongated tube.

Aspects of the systems and methods described may have one or more of thefollowing advantages: a continuous offset staved cold water pipe islighter than segmented pipe construction; a continuous offset stavedcold water pipe has less frictional losses than a segmented pipe;individual staves can be sized for easy transportation to the OTEC plantoperational site; staves can be constructed to desired buoyancycharacteristics; OTEC power production requires little to no fuel costsfor energy production; the low pressures and low temperatures involvedin the OTEC heat engine reduce component costs and require ordinarymaterials compared to the high-cost, exotic materials used in highpressure, high temperature power generation plants; plant reliability iscomparable to commercial refrigeration systems, operating continuouslyfor several years without significant maintenance; reduced constructiontimes compared to high pressure, high temperature plants; and safe,environmentally benign operation and power production. Additionaladvantages may include, increased net efficiency compared to traditionalOTEC systems, lower sacrificial electrical loads; reduced pressure lossin warm and cold water passages; modular components; less frequentoff-grid production time; minimal heave and reduced susceptibility towave action; discharge of cooling water below surface levels, intake ofwarm water free from interference from cold water discharge.

Cold water pipe assemblies and methods of connecting cold water pipeassemblies to spar structures described herein can create strong, rigidconnections while allowing the cold water pipe to have increasedflexibility over certain conventional cold water pipes by creatingmulti-sectional cold water pipes where different sections have varyingstiffness to transfer loads throughout the cold water pipe.

Cold water pipe assemblies and methods of connecting cold water pipeassemblies to spar structures described herein can also be used tocreate cold water pipes that can be attached to and detached from sparstructures faster and easier than certain conventional cold water pipes.

Cold water pipe assemblies and methods of cold water pipe attachment tospar structures described herein can be used to create a cold water pipeto spar structure attachment interface that is easier to align andprovide better sealing than certain conventional cold water pipes.

The details of one or more embodiments of the disclosure are set forthin the accompanying drawings and the description below. Other aspects,features, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an exemplary prior-art OTEC heat engine.

FIG. 2 illustrates an exemplary prior-art OTEC power plant.

FIG. 3 illustrates an OTEC structure.

FIG. 3A illustrates an OTEC structure.

FIG. 4 illustrates an offset staved pipe of an OTEC structure.

FIG. 5 illustrates a detailed image of an offset stave pattern.

FIG. 6 illustrates a cross sectional view of an offset staved cold waterpipe.

FIGS. 7A-C illustrate various views of individual staves.

FIG. 8 illustrates a tongue and groove arrangement of an individualstave.

FIGS. 9A-B illustrate a positive snap lock between two staves.

FIG. 10 illustrates an offset staved cold water pipe incorporating areinforcing strake.

FIG. 11 illustrates a method of cold water pipe construction.

FIG. 12 illustrates a prior-art example of a gimbaled pipe connection.

FIG. 13 illustrates a cold water pipe connection.

FIG. 14 illustrates a cold water pipe connection.

FIG. 15 illustrates a cold water pipe connection method.

FIG. 16 illustrates a cold water pipe connection with a flexible coldwater pipe.

FIG. 17 illustrates a cold water pipe connection.

FIG. 18 illustrates a cold water pipe with a lifting collar.

FIG. 19 illustrates a cut-away perspective view of a heat exchangerdeck.

FIG. 20 illustrates a deck plan of a heat exchanger deck.

FIG. 21 illustrates a cabinet heat exchanger.

FIG. 22A illustrates a conventional heat exchange cycle.

FIG. 22B illustrates a cascading multi-stage heat exchange cycle.

FIG. 22C illustrates a hybrid cascading multi-stage heat exchange cycle.

FIG. 22D illustrates the evaporator pressure drop and associate powerproduction.

FIGS. 23A-B illustrate an exemplary OTEC heat engine.

FIG. 24 illustrates a cold water pipe divided into three sections.

FIG. 25 illustrates a first section of the cold water pipe of FIG. 24.

FIG. 26 illustrates a cross-sectional view of a mating ring and upperface plates of the upper section of the cold water pipe of FIG. 24.

FIG. 27 illustrates a cross-sectional view of a spar interface sectionof the upper section of FIG. 24.

FIG. 28 illustrates an interface joint between the upper and middle coldwater pipe sections of FIG. 24.

FIG. 29 illustrates the middle section of the cold water pipe of FIG.24.

FIG. 30 illustrates a longitudinal joint of two adjoining pipe staves ofthe middle section of FIG. 29.

FIG. 31 illustrates an end joint of two adjoining pipe staves of themiddle section of FIG. 29.

FIG. 32 illustrates a lower section of the cold water pipe of FIG. 24.

Like reference symbols in the various drawings indicate like elementsunless otherwise indicated.

DETAILED DESCRIPTION

This disclosure relates to electrical power generation using OceanThermal Energy Conversion (OTEC) technology. Aspects of the disclosurerelate to a floating OTEC power plant having improved overallefficiencies with reduced parasitic loads, greater stability, lowerconstruction and operating costs, and improved environmental footprintover previous OTEC power plants. Other aspects include large volumewater conduits that are integral with the floating structure. Modularityand compartmentation of the multi-stage OTEC heat engine reducesconstruction and maintenance costs, limits off-grid operation andimproves operating performance. Still further aspects provide for afloating platform having integrated heat exchange compartments andprovides for minimal movement of the platform due to wave action. Theintegrated floating platform may also provide for efficient flow of thewarm water or cool water through the multi-stage heat exchanger,increasing efficiency and reducing the parasitic power demand. Aspectsof the systems and methods described promote a neutral thermal footprintby discharging warm and cold water at appropriate depth/temperatureranges. Energy extracted in the form of electricity reduces the bulktemperature to the ocean.

OTEC is a process that uses heat energy from the sun that is stored inthe Earth's oceans to generate electricity. OTEC utilizes thetemperature difference between the warmer, top layer of the ocean andthe colder, deep ocean water. Typically this difference is at least 36°F. (20° C.). These conditions exist in tropical areas, roughly betweenthe Tropic of Capricorn and the Tropic of Cancer, or even 20° north andsouth latitude. The OTEC process uses the temperature difference topower a Rankine cycle, with the warm surface water serving as the heatsource and the cold deep water serving as the heat sink. Rankine cycleturbines drive generators which produce electrical power.

FIG. 1 illustrates a typical OTEC Rankine cycle heat engine 10 whichincludes warm sea water inlet 12, evaporator 14, warm sea water outlet15, turbine 16, cold sea water inlet 18, condenser 20, cold sea wateroutlet 21, working fluid conduit 22 and working fluid pump 24.

In operation, heat engine 10 can use any one of a number of workingfluids, for example commercial refrigerants such as ammonia. Otherworking fluids can include propylene, butane, R-22 and R-134a. Othercommercial refrigerants can be used. Warm sea water betweenapproximately 75° and 85° F., or more, is drawn from the ocean surfaceor just below the ocean surface through warm sea water inlet 12 and inturn warms the ammonia working fluid passing through evaporator 14. Theammonia boils to a vapor pressure of approximately 9.3 atm. The vapor iscarried along working fluid conduit 22 to turbine 16. The ammonia vaporexpands as it passes through the turbine 16, producing power to drive anelectric generator 25. The ammonia vapor then enters condenser 20 whereit is cooled to a liquid by cold sea water drawn from a deep ocean depthof approximately 3000 ft. The cold sea water enters the condenser at atemperature of approximately 40° F. The vapor pressure of the ammoniaworking fluid at the temperature in the condenser 20, approximately 51°F., is 6.1 atm. Thus, a significant pressure difference is available todrive the turbine 16 and generate electric power. As the ammonia workingfluid condenses, the liquid working fluid is pumped back into theevaporator 14 by working fluid pump 24 via working fluid conduit 22.

The heat engine 10 of FIG. 1 is essentially the same as the Rankinecycle of most steam turbines, except that OTEC differs by usingdifferent working fluids and lower temperatures and pressures. The heatengine 10 of the FIG. 1 is also similar to commercial refrigerationplants, except that the OTEC cycle is run in the opposite direction sothat a heat source (e.g., warm ocean water) and a cold heat sink (e.g.,deep ocean water) are used to produce electric power.

FIG. 2 illustrates the typical components of a floating OTEC facility200, which include: the vessel or platform 210, warm sea water inlet212, warm water pump 213, evaporator 214, warm sea water outlet 215,turbine-generator 216, cold water pipe 217, cold sea water inlet 218,cold water pump 219, condenser 220, cold sea water outlet 221, workingfluid conduit 22, working fluid pump 224, and pipe connections 230. OTECfacility 200 can also include electrical generation, transformation andtransmission systems, position control systems such as propulsion,thrusters, or mooring systems, as well as various auxiliary and supportsystems (for example, personnel accommodations, emergency power, potablewater, black and grey water, firefighting, damage control, reservebuoyancy, and other common shipboard or marine systems).

Implementations of OTEC power plants utilizing the basic heat engine andsystem of FIGS. 1 and 2 have a relatively low overall efficiency of 3%or below. Because of this low thermal efficiency, OTEC operationsrequire the flow of large amounts of water through the power system perkilowatt of power generated. This in turn requires large heat exchangershaving large heat exchange surface areas in the evaporator andcondensers.

Such large volumes of water and large surface areas require considerablepumping capacity in the warm water pump 213 and cold water pump 219,reducing the net electrical power available for distribution to ashore-based facility or on board industrial purposes. Moreover, thelimited space of most surface vessels does not easily facilitate largevolumes of water directed to and flowing through the evaporator orcondenser. Indeed, large volumes of water require large diameter pipesand conduits. Putting such structures in limited space requires multiplebends to accommodate other machinery. And the limited space of typicalsurface vessels or structures does not easily facilitate the large heatexchange surface area required for maximum efficiency in an OTEC plant.Thus the OTEC systems and vessel or platform have traditional been largeand costly. This has lead to an industry conclusion that OTEC operationsare a high cost, low yield energy production option when compared toother energy production options using higher temperatures and pressures.

Aspects of the systems and methods described address technicalchallenges in order to improve the efficiency of OTEC operations andreduce the cost of construction and operation.

The vessel or platform 210 requires low motions to minimize dynamicforces between the cold water pipe 217 and the vessel or platform 210and to provide a benign operating environment for the OTEC equipment inthe platform or vessel. The vessel or platform 210 should also supportcold sea water inlet 218 and warm sea water inlet 212 volume flows,bringing in sufficient cold and warm water at appropriate levels toprovide OTEC process efficiency. The vessel or platform 210 should alsoenable cold and warm water discharge via cold water outlets 221 and warmwater outlets 215 well below the waterline of vessel or platform 210 toavoid thermal recirculation into the ocean surface layer. Additionally,the vessel or platform 210 should survive heavy weather withoutdisrupting power generating operations.

The OTEC heat engine 10 should utilize a highly efficient thermal cyclefor maximum efficiency and power production. Heat transfer in boilingand condensing processes, as well as the heat exchanger materials anddesign, limit the amount of energy that can be extracted from each poundof warm seawater. The heat exchangers used in the evaporator 214 and thecondenser 220 require high volumes of warm and cold water flow with lowhead loss to minimize parasitic loads. The heat exchangers also requirehigh coefficients of heat transfer to enhance efficiency. The heatexchangers can incorporate material and design that may be tailored tothe warm and cold water inlet temperatures to enhance efficiency. Theheat exchanger design should use a simple construction method withminimal amounts of material to reduce cost and volume.

Turbo generators 216 should be highly efficient with minimal internallosses and may also be tailored to the working fluid to enhanceefficiency

FIG. 3 illustrates an implementation that enhances the efficiency ofprevious OTEC power plants and overcomes many of the technicalchallenges associated therewith. This implementation comprises a sparfor the vessel or platform, with heat exchangers and associated warm andcold water piping integral to the spar.

OTEC Spar 310 houses an integral multi-stage heat exchange system foruse with an OTEC power generation plant. Spar 310 includes a submergedportion 311 below waterline 305. Submerged portion 311 comprises warmwater intake portion 340, evaporator portion 344, warm water dischargeportion 346, condenser portion 348, cold water intake portion 350, coldwater pipe 217, cold water discharge portion 352, machinery deck portion354. A deck house 360 sets atop the spar housing the electricalswitchyard, auxiliary and emergency machinery and systems, boat handlingequipment, and manned spaces such as office, accommodations,communications center and control rooms.

FIG. 3A illustrates an exemplary machinery layout of the present systemsand methods described, including warm water intake portion 340, warmwater pump room 341, stacked evaporator portion 344, turbine generator349, stacked condenser portion 348, cold water intake portion 350, andcold water pump room 351.

In operation, warm sea water of between 75° F. and 85° F. is drawnthrough warm water intake portion 340 and flows down the spar thoughstructurally integral warm water conduits not shown. Due to the highvolume water flow requirements of OTEC heat engines, the warm waterconduits direct flow to the evaporator portion 344 of between 500,000gpm and 6,000,000 gpm. Such warm water conduits have a diameter ofbetween 6 ft and 35 ft, or more. Due to this size, the warm waterconduits are vertical structural members of spar 310. Warm waterconduits can be large diameter pipes of sufficient strength tovertically support spar 310. Alternatively, the warm water conduits canbe passages integral to the construction of the spar 310.

Warm water then flows through the evaporator portion 344 which housesone or more stacked, multi-stage heat exchangers for warming a workingfluid to a vapor. The warm sea water is then discharged from spar 310via warm water discharge 346. Warm water discharge can be located ordirected via a warm water discharge pipe to a depth at or close to anocean thermal layer that is approximately the same temperature as thewarm water discharge temperature to minimize environmental impacts. Thewarm water discharge can be directed to a sufficient depth to reduce thelikelihood of thermal recirculation with either the warm water intake orcold water intake.

Cold sea water is drawn from a depth of between 2500 and 4200 ft, ormore, at a temperature of approximately 40° F., via cold water pipe 217.The cold sea water enters spar 310 via cold water intake portion 350.Due to the high volume water flow requirements of OTEC heat engines, thecold sea water conduits direct flow to the condenser portion 348 ofbetween 500,000 gpm and 3,500,000 gpm. Such cold sea water conduits havea diameter of between 6 ft and 35 ft, or more. Due to this size, thecold sea water conduits are vertical structural members of spar 310.Cold water conduits can be large diameter pipes of sufficient strengthto vertically support spar 310. Alternatively, the cold water conduitscan be passages integral to the construction of the spar 310.

Cold sea water then flows upward to stacked multi-stage condenserportion 348, where the cold sea water cools a working fluid to a liquid.The cold sea water is then discharged from spar 310 via cold sea waterdischarge 352. Cold water discharge can be located or directed via acold sea water discharge pipe to depth at or close to an ocean thermallayer that is approximately the same temperature as the cold sea waterdischarge temperature. The cold water discharge can be directed to asufficient depth to reduce the likelihood of thermal recirculation witheither the warm water intake or cold water intake.

Machinery deck portion 354 can be positioned vertically between theevaporator portion 344 and the condenser portion 348. Positioningmachinery deck portion 354 beneath evaporator portion 344 allows nearlystraight line warm water flow from intake, through the multi-stageevaporators, and to discharge. Positioning machinery deck portion 354above condenser portion 348 allows nearly straight line cold water flowfrom intake, through the multi-stage condensers, and to discharge.Machinery deck portion 354 includes turbo-generators 356. In operation,warm working fluid heated to a vapor from evaporator portion 344 flowsto one or more turbo generators 356. The working fluid expands in turbogenerator 356 thereby driving a turbine for the production of electricalpower. The working fluid then flows to condenser portion 348 where it iscooled to a liquid and pumped to evaporator portion 344.

The performance of heat exchangers is affected by the availabletemperature difference between the fluids as well as the heat transfercoefficient at the surfaces of the heat exchanger. The heat transfercoefficient generally varies with the velocity of the fluid across theheat transfer surfaces. Higher fluid velocities require higher pumpingpower, thereby reducing the net efficiency of the plant. A hybridcascading multi-stage heat exchange system facilitates lower fluidvelocities and greater plant efficiencies. The stacked hybrid cascadeheat exchange design also facilitates lower pressure drops through theheat exchanger. The vertical plant design facilitates lower pressuredrop across the whole system. A hybrid cascading multi-stage heatexchange system is described in U.S. Patent Publication No. US2011/0173979 A1, entitled “Ocean Thermal Energy Conversion Plant,” filedon Jan. 21, 2010, the entire contents of which are incorporated hereinby reference.

Cold Water Pipe

As described above, OTEC operations require a source of cold water at aconstant temperature. Variations in the cooling water can greatlyinfluence the overall efficiency of the OTEC power plant. As such, waterat approximately 40° F. is drawn from depths of between 2700 ft and 4200ft or more. A long intake pipe is needed to draw this cold water to thesurface for use by the OTEC power plant. Such cold water pipes have beenan obstacle to commercially viable OTEC operations because of the costin constructing a pipe of suitable performance and durability.

Such cold water pipes have been an obstacle to commercially viable OTECoperations because of the cost in constructing a pipe of suitableperformance and durability. OTEC requires large volumes of water atdesired temperatures in order to ensure maximum efficiency in generatingelectrical power. Previous cold water pipe designs specific to OTECoperations have included a sectional construction. Cylindrical pipesections were bolted or mechanically joined together in series until asufficient length was achieved. Pipe sections were assembled near theplant facility and the fully constructed pipe was then upended andinstalled. This approach had significant drawbacks including stress andfatigue at the connection points between pipe sections. Moreover, theconnection hardware added to the overall pipe weight, furthercomplicating the stress and fatigue considerations at the pipe sectionconnections and the connection between the fully assembled CWP and theOTEC platform or vessel.

The cold water pipe (“CWP”) is used to draw water from the cold waterreservoir at an ocean depth of between 2700 ft and 4200 ft or more. Thecold water is used to cool and condense to a liquid the vaporous workingfluid emerging from the power plant turbine. The cold water pipe and itsconnection to the vessel or platform are configured to withstand thestatic and dynamic loads imposed by the pipe weight, the relativemotions of the pipe and platform when subjected to wave and currentloads of up to 100-year-storm severity, and the collapsing load inducedby the water pump suction. The cold water pipe is sized to handle therequired water flow with low drag loss, and is made of a material thatis durable and corrosion resistant in sea water.

The cold water pipe length is defined by the need to draw water from adepth where the temperature is approximately 40° F. The CWP length canbe between 2000 feet and 4000 ft or more. In aspects of the presentsystems and methods described, the cold water pipe can be approximately3000 feet in length.

The cold water pipe diameter is determined by the power plant size andwater flow requirements. The water flow rate through the pipe isdetermined by the desired power output and OTEC power plant efficiency.The cold water pipe can carry cold water to the cold water conduit ofthe vessel or platform at a rate of between 500,000 gpm and 3,500,000gpm, or more. Cold water pipe diameters can be between 6 feet and 35feet or more. In aspects of the present systems and methods described,the cold water pipe diameter is approximately 31 feet in diameter.

Previous cold water pipe designs specific to OTEC operations haveincluded a sectional construction. Cylindrical pipe sections of between10 and 80 feet in length were bolted or joined together in series untila sufficient length was achieved. Using multiple cylindrical pipesections, the cold water pipe could be assembled near the plant facilityand the fully constructed pipe could be upended and installed. Thisapproach had significant drawbacks including stress and fatigue at theconnection points between pipe sections. Moreover, the connectionhardware added to the overall pipe weight, further complicating thestress and fatigue considerations at the pipe section connections andthe connection between the fully assembled cold water pipe and the OTECplatform or vessel.

Referring to FIG. 4 a continuous offset staved cold water pipe is shown.The cold water pipe 217 is free of sectional joints as in previous coldwater pipe designs, instead utilizing an offset stave construction. Coldwater pipe 217 includes a top end portion 452 for connection to thesubmerged portion of the floating OTEC platform 411. Opposite top endportion 452 is bottom portion 454, which can include a ballast system,an anchoring system, and/or an intake screen.

Cold water pipe 217 comprises a plurality of offset staves assembled toform a cylinder. In some embodiments, the plurality of offset stavesincludes alternating multiple first staves 465 and multiple secondstaves 467. Each first stave includes a top edge 471 and a bottom edge472. Each second stave includes a top edge 473 and a bottom edge 474. Insome embodiments, second stave 467 is vertically offset from an adjacentfirst stave portion 465 such that top edge 473 (of second stave portion467) is between 3% and 97% vertically displaced from the top edge 471(of first stave portion 465). The offset between adjacent staves can beapproximately, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50% or more.

FIG. 5 illustrates a detail view of an offsetting stave pattern of anaspect of the present systems and methods described. The patternincludes multiple first staves 465, each having a top edge portion 471,bottom edge portion 472, connected edge 480 and offset edge 478. Thepattern also includes multiple second staves 467, each having a top edgeportion 473, a bottom edge portion 474, connected edge 480, and offsetedge 479. In forming the cold water pipe, first stave section 465 isjoined to second stave section 467 such that connected edge 480 isapproximately 3% to 97% of the length of first stave section 465 whenmeasured from the top edge 471 to the bottom edge 472. In an aspect,connected edge 480 is approximately 50%, 55%, 60%, 65%, 70%, 75%, 80%,85%, or 90% of the length of the stave.

It will be appreciated that in a fully constructed pipe, first stave 465can be joined to second stave 467 along connected edge 480. First stave465 can also be connected to additional staves along offset edge 478,including an additional first stave portion, an additional second staveportion, or any other stave portion. Similarly, second stave 467 can bejoined to first stave portion along connected edge 480. And second stave467 can be joined to another stave along offset edge 479, including anadditional first stave portion, an additional second stave portion, orany other stave portion.

In aspects, the connected edge 480 between the multiple first staves 465and the multiple second staves 467 can be a consistent length orpercentage of the stave length for each stave about the circumference ofthe pipe. The connected edge 480 between the multiple first staves 465and the multiple second staves 465 can be a consistent length orpercentage of the stave length for each stave along the longitudinalaxis of the cold water pipe 451. In further aspects the connected edge480 can vary in length between alternating first staves 465 and secondstaves 467.

As illustrated in FIG. 5, first stave 465 and second stave 467 have thesame dimensions. In aspects, first stave 465 can be between 30 and 130inches wide or more, 30 to 60 feet long, and between 1 and 24 inchesthick. In an aspect the stave dimensions can be approximately 80 incheswide, 40 feet long, and 4 to 12 inches thick. Alternatively, first stave465 can have a different length or width from second stave 467.

FIG. 6 illustrates a cross sectional view of cold water pipe 217 showingalternating first staves 465 and second staves 467. Each stave includesan inner surface 485 and an outer surface 486. Adjacent staves arejoined along connected surface 480. Any two connected surfaces onopposite sides of a single stave define an angle α. The angle α isdetermined by dividing 360° by the total number of staves. In an aspect,α can be between 1° and 36°. In an aspect α can be 22.5° for a 16 stavepipe or 11.25° for a 32 stave pipe.

Individual staves of cold water pipe 217 can be made from polyvinylchloride (PVC), chlorinated polyvinyl chloride (CPVC), fiber reinforcedplastic (FRP), reinforced polymer mortar (RPMP), polypropylene (PP),polyethylene (PE), cross-linked high-density polyethylene (PEX),polybutylene (PB), acrylonitrile butadiene styrene (ABS); polyurethane,polyester, fiber reinforced polyester, nylon reinforce polyester, vinylester, fiber reinforced vinyl ester, nylon reinforced vinyl ester,concrete, ceramic, or a composite of one or more thereof. Individualstaves can be molded, extruded, or pulltruded using standardmanufacturing techniques. In one aspect, individual staves arepulltruded to the desired shape and form and comprise a fiber or nylonreinforced vinyl ester. Vinyl esters are available from Ashland Chemicalof Covington, Ky.

In some embodiments, staves are bonded to adjacent staves using asuitable adhesive. A flexible resin can be used to provide a flexiblejoint and uniform pipe performance. In aspects of the systems andmethods described, staves comprising a reinforced vinyl ester are bondedto adjacent staves using a vinyl ester resin. Methacrylate adhesives canalso be used, such as MA560-1 manufactured by Plexis StructuralAdhesives of Danvers, Mass.

Referring to FIGS. 7A-7C, various stave constructions are shown whereinan individual stave 465 includes a top edge 471, a bottom edge 472 andone or more voids 475. Void 475 can be hollow, filled with water, filledwith a resin, filled with an adhesive, or filled with a foam material,such as syntactic foam. Syntactic foam is a matrix of resin and smallglass beads. The beads can either be hollow or solid. Void 475 can befilled to influence the buoyancy of the stave and/or the cold water pipe451. FIG. 7A illustrates a single void 475. In some embodiments,multiple voids 475 can be equally spaced along the length of the stave,as illustrated in FIG. 7B. In some embodiments, one or more voids 475are placed toward one end of the stave, for example toward the bottomedge 472, as illustrated in FIG. 7C.

Referring to FIG. 8, each individual stave 465 can include a top edge471, a bottom edge 472, a first longitudinal side 491 and a secondlongitudinal side 492. In some embodiments, longitudinal side 491includes a joinery member, such as tongue 493. The joinery member canalternatively include, biscuits, half-lap joints, or other joinerystructures. Second longitudinal side 492 includes a mating joinerysurface, such as groove 494. In use, the first longitudinal side 491 ofa first stave mates or joins with the second longitudinal side 492 of asecond stave. Though not shown, joining structures, such as tongue andgroove, or other structures can be used at the top edge 471 and thebottom edge 472 to join a stave to a longitudinally adjacent stave.

In aspects of the systems and methods described, first longitudinal sidecan include a positive snap lock connection 491 for mating engagementwith second longitudinal side 492. Positive snap lock connections orsnap lock connections are generally described in U.S. Pat. No.7,131,242, incorporated herein by reference in its entirety. The entirelength of tongue 493 can incorporate a positive snap lock or portions oftongue 493 can include a positive snap lock Tongue 493 can include snaprivets. It will be appreciated that where tongue 493 includes a snaplocking structure, an appropriate receiving structure is provided on thesecond longitudinal side having groove 494.

FIG. 9A illustrates an exemplary positive snap lock system, wherein maleportion 970 includes collar 972. Male portion 970 mechanically engageswith receiving portion 975 with include recessed collar mount 977. Inuse, male portion 970 is inserted into receiving portion 975 such thatcollar portion 972 engages recessed collar mount 977, there by allowinginsertion of the male portion 970 but preventing its release orwithdrawal.

Positive snap locking joints between staved portions of the offsetstaved pipe can be used to mechanically lock two staved portionstogether. The positive snap lock joints can be used alone or incombination with a resin or adhesive. In some embodiments, a flexibleresin is used in combination with the positive snap lock joint.

FIG. 9B illustrates another exemplary positive snap lock system. Theillustrated joint is self-supporting so that it retains the staves inboth the radial and circumferential direction. The lip of piece 981locks under the shelf of piece 979 on the inner surface of the stave,holding the two pieces 979, 981 aligned along the longitudinal edge.There is no such shelf on the outer edge which is tapered, according tothe required angle based on the number of staves. As the two pieces 979,981 come together to mate along the longitudinal edge, the snap member983 clicks into the detent and holds the two pieces together radially,and circumferentially because of the slight angularity of the clip inthe detent. The void near the snap 983 is filled with adhesive prior tomating the two staves so that it will expand and fill completely anyvoid between the staves and seal the pipe from leaking in or out.

FIG. 10 illustrates a cold water pipe 217 having an offset staveconstruction comprising multiple alternating first staves 465 and secondstaves 467 and further comprising a spirally wound ribbon 497 coveringat least a portion of the outer surface of cold water pipe 451. In someembodiments, the ribbon is continuous from the bottom portion 454 ofcold water pipe 217 to the top portion 452 of the cold water pipe 217.In other embodiments, the ribbon 497 is provided only in those portionsof pipe 217 that experience vortex shedding due to movement of waterpast the cold water pipe 217. Ribbon 497 provides radial andlongitudinal support to cold water pipe 217. Ribbon 497 also preventsvibration along the cold water pipe and reduces vortex shedding due toocean current action.

Ribbon 497 can be the same thickness and width as an individual stave ofcold water pipe 451 or can be two, three, four or more time thethickness and up to 10 times (e.g., 2, 3, 4, 5, 6, 7 8, 9 or 10 times)the width of an individual stave.

Ribbon 497 can be mounted on the outside surface of the cold water pipeso as to lay substantially flat along the outside surface. In someembodiments, ribbon 497 can protrude outwardly from the outside surfaceof cold water pipe 451 so as to form a spirally wound strake. In someembodiments, a fin, blade or foil can be attached to various portions ofribbon or strake 497. Such fins can form a helix wounding around aportion of the cold water pipe or winding the entire length of the coldwater pipe. Fins can be angled and provide about the strake in anynumber to prevent vortex conditions caused by the cold water pipe. Insome embodiments, the fins can protrude from the pipe surface a distanceof between 1/32 and ⅓ of the pipe diameter (e/g, about 1/32 of the pipediameter, about 1/16^(th) the pipe diameter, about ⅛^(th) the pipediameter, about 1/7^(th) the pipe diameter, about ⅙^(th) the pipediameter, about ⅕^(th) the pipe diameter, about ¼ the pipe diameter, andabout ⅓^(rd) the pipe diameter).

Ribbon 497 can be of any suitable material compatible with the materialof the multiple staves forming cold water pipe 451, including: polyvinylchloride (PVC), chlorinated polyvinyl chloride (CPVC), fiber reinforcedplastic (FRP), reinforced polymer mortar (RPMP), polypropylene (PP),polyethylene (PE), cross-linked high-density polyethylene (PEX),polybutylene (PB), acrylonitrile butadiene styrene (ABS); polyurethane,polyester, fiber reinforced polyester, vinyl ester, reinforced vinylester, concrete, ceramic, or a composite of one or more thereof. Ribbon497 can be molded, extruded, or pulltruded using standard manufacturingtechniques. In some embodiments, ribbon 497 is pulltruded to the desiredshape and form and comprises a fiber or nylon reinforced vinyl estersimilar to that used with the staves of cold water pipe 451. Ribbon 497can be joined to the cold water pipe 217 using a suitable adhesive orresin including the resins of any of the materials above.

In some embodiments, ribbon 497 is not continuous along the length ofcold water pipe 451. In some embodiments, ribbon 497 is not continuousabout the circumference of cold water pipe 217. In some embodiments,ribbon 497 includes vertical strips adhered to the outside surface ofthe cold water pipe 217. In some embodiments, where radial or otherstructural support is required, ribbon 497 can be a circumferentialsupport member around the outside surface of the cold water pipe.

Ribbon 497 can be adhesively bonded or adhered to the outside surface ofthe cold water pipe, using a suitable flexible adhesive. In someembodiments, ribbon 497 can be mechanically coupled to the outsidesurface of the cold water pipe 217 using multiple positive snap locks.

With regard to FIG. 11, an exemplary method of assembling a cold waterpipe provides for the efficient transport and assembly of the cold waterpipe 217. Vertical cylindrical pipe sections are assembled by aligning1110 alternating first and second stave portions to have the desiredoffset as described above. The first and second stave portions are thenjoined 1120 to form a cylindrical pipe section. The offset first andsecond staves can be joined using any of a variety of joining methods.In some embodiments, the multiple offset first and second stave portionsare joined using a tongue and groove arrangement and a flexibleadhesive. In some embodiments the multiple first and second stavedportions are joined using a mechanical positive snap lock. A combinationof tongue and groove, snap lock mechanisms, and flexible adhesives canbe used.

After joining 1120 the multiple first and second stave portions to forma cylindrical pipe section having offset first and second staveportions, a retaining band, inflatable sleeve or other jig can beattached 1122 to the cylindrical pipe section to provide support andstability to the pipe section. The steps of aligning 1110 and joining1120 multiple offset first and second stave portions can be repeated1124 to form any number of prefabricated cylindrical pipe sections. Itwill be appreciated that the cylindrical pipe section can beprefabricated at the OTEC plant facility or remotely and thentransported to the OTEC plant facility for additional construction toform the fully assembled cold water pipe 451.

Having assembled at least two cylindrical pipe sections having offsetstaves, an upper and lower cylindrical pipe sections are joined 1126 andthe offset staves of each pipe section are aligned. A flexible adhesivecan be applied 1130 to the butt joint of the offset staves of the upperand lower cylindrical pipe sections. The staves of the two pipe sectionscan be joined using a variety of end butt joints including biscuitjoinery. In an aspect, the offset staves of the upper and lowercylindrical pipe portions can be provided with aligning joining voidswhich in turn can be filled with a flexible adhesive.

Gaps in and joints between pipe sections or between and individualstaves can be filled 1132 with additional flexible resin. Once the twopipe sections have been joined and the resin applied where needed thetwo pipe sections are allowed to cure 1134.

The retaining band is then removed 1136 from the lower pipe section anda spirally wound strake is attached thereto. The spirally wound strakecan be attached using adhesive bonding, mechanical bonding, for examplepositive snap locks, or a combination of the adhesive and mechanicalbonding.

In some aspects of methods described, after the spiral strake isattached to the lower pipe section, the entire pipe assembly can beshifted, for example lowered, so that the previous upper pipe portionbecomes the new lower pipe portion, 1138. Then a new upper cylindricalpipe section is assembled 1140 in a similar manner as described above.That is, first and second stave portions are aligned 1142 to achieve thedesired offset. The first and second stave portions are then joined 1144to form a new cylindrical pipe section, e.g., new upper pipe section. Aspreviously mentioned, a retaining band, inflatable sleeve or other jigcan be used to provide support and stability to the cylindrical pipesection during construction of the cold water pipe 217.

Having assembled new upper pipe section 1144, the offset staves of thenew lower pipe section and the new upper pipe section are aligned anddrawn together 1146. Adhesive or flexible resin is applied 1148 to theend butt joints as described above, for example in conjunction withbiscuit joinery or with aligning joining voids. Any gaps between the newlower pipe section and the new upper pipe section or between any twostave portions can be filled 1150 with additional flexible resin. Theentire assembly can then be left to cure 1152. The retaining jig can beremoved 1154 as before and the spiral strake can be attached to the newlower portion. And, as before, the entire pipe assembly can be shiftedto provide for the next cylindrical pipe section. In this manner, themethod can be repeated until the desired pipe length is achieved.

It will be appreciated that joining cylindrical pipe sections havingoffset staves can be accomplished in a number of manners consistent withthe present systems and methods described. The method of joining offsetstaves provides for a continuous pipe without the need for bulky, heavyor interfering joining hardware between the pipe segments. As such acontinuous pipe having nearly uniform material properties, includingflexibility and rigidity, is provided.

Example

A cold water pipe assembly is provided that facilitates on siteconstruction of a continuous, offset staved pipe of approximately 3000feet. Additionally the staved design accounts for adverse shipping andhandling loads traditionally experienced by segmented pipe construction.For example towing and upending of traditionally constructed segmentedcold water pipes imposes hazardous loads on the pipe.

Staved construction allows offsite manufacturing of multiple staves of40 ft to 50 ft lengths. Each stave is approximately 52 inches wide and 4inches to 12 inches thick. The staves can be shipped in stacks orcontainers to the offshore platform and the cold water pipe can then beconstructed on the platform from the multiple staves. This eliminatesthe need for a separate facility to assemble pipe sections.

The stave portions can be constructed from a nylon reinforced vinylester having a modulus of elasticity of between about 66,000 psi and165,000 psi. The stave portions can have an ultimate strength of betweenabout 15,000 psi and 45,000 psi, with a tensile strength between about15,000 psi to 45,000 psi. In an aspect, the stave portions can have amodulus of elasticity of 150,000 psi, an ultimate strength of 30,000 psiand a yield strength of 30,000 psi, such that the installed cold waterpipe behaves similar to a hose rather than a purely rigid pipe. This isadvantageous in storm conditions as the pipe is more flexible and avoidscracking or breaking. In an aspect, the pipe can deflect approximatelytwo diameters from center at the unconnected lower end. Deflection atthe unconnected lower end should not be so great as to interfere withthe mooring system of the OTEC power plant or any other underwatersystems involved in plant operations.

The cold water pipe connects to the bottom portion of the OTEC powerplant. More specifically, the cold water pipe connects using a dynamicbearing with the bottom portion of the OTEC spar of FIG. 3. Cold waterpipe connections in OTEC applications are described in Section 4.5 ofAvery & Wu, “Renewable Energy from the Ocean, a Guide to OTEC,” OxfordUniversity Press, 1994, incorporated herein by reference in itsentirety.

One of the significant advantages of using the spar buoy as the platformis that doing so results in relatively small rotations between the sparitself and the cold water pipe even in the most severe 100-year stormconditions. In addition the vertical and lateral forces between the sparand the cold water pipe are such that the downward force between thespherical ball and its seat keeps the bearing surfaces in contact at alltimes. Because this bearing that also acts as the water seal does notcome out of contact with its mating spherical seat there is no need toinstall a mechanism to hold the cold water pipe in place vertically.This helps to simplify the spherical bearing design and also minimizesthe pressure losses that would otherwise be caused by any additionalcold water pipe pipe restraining structures or hardware. The lateralforces transferred through the spherical bearing are also low enoughthat they can be adequately accommodated without the need for verticalrestraint of the cold water pipe.

Cold water is drawn through the cold water pipe via one or more coldwater pumps such and flows via one or more cold water passages orconduits to the condenser portion of a multi-stage OTEC power plant.

Further details of cold water pipe construction and performance aredescribed in U.S. Patent Publication No. US 2011/0173978, entitled“Ocean Thermal Energy Conversion Power Plant Cold Water Pipe,” filed onJan. 21, 2010, the entire contents of which are incorporated herein byreference.

Cold Water Pipe Connection

The connection between the cold water pipe 217 and the spar platform 311presents construction, maintenance and operational challenges. Forexample, the cold water pipe is a 2000 ft to 4000 ft vertical columnsuspended in the dynamic ocean environment. The platform or vessel towhich the cold water pipe connects is also floating in the dynamic oceanenvironment. Moreover, the pipe is ideally connected below thewaterline, and in some aspects, well below the waterline and close tothe bottom of the vessel. Maneuvering the fully assembled pipe into theproper position and a securing the pipe to the vessel or platform is adifficult task.

The cold water pipe connection supports the static weight of the pipesuspended from the platform and accounts for the dynamic forces betweenthe platform and the suspended pipe due to wave action, pipe vibration,and pipe movement.

Various OTEC cold water pipe connections, including gimbal, ball andsocket, and universal connections, are disclosed in Section 4.5 of“Renewable Energy from the Ocean, a Guide to OTEC” William Avery andChih Wu, Oxford University Press, 1994, incorporated herein byreference. Only the gimbal connection was operationally tested andincluded a two-axis gimbal allowing for 30° of rotation. As described inAvery and Wu, in the plane of the gimbal, a spherical shell formed thetop of the pipe. A cylindrical cap with a flat ring of nylon and Teflonprovided a sliding seal between the cold water in the pipe and thesurrounding platform structure. The gimbaled pipe connection isillustrated in FIG. 12.

Previous cold water pipe connections were designed for traditional hullforms and platforms that exhibit greater vertical displacement due toheave and wave action than spar platforms. One of the significantadvantages of using the spar buoy as the platform is that doing soresults in relatively small rotations between the spar itself and theCWP even in the most severe 100-year storm conditions. In addition thevertical and lateral forces between the spar and the cold water pipe aresuch that the downward force between the spherical ball and its seatkeeps the bearing surfaces in contact at all times. In some embodiments,the downward force between the cold water pipe and the connectionbearing surface is between 0.4 g and 1.0 g. Because this bearing thatalso acts as the water seal does not come out of contact with its matingspherical seat there is no need to install a mechanism to hold the coldwater pipe in place vertically. This helps to simplify the sphericalbearing design and also minimizes the pressure losses that wouldotherwise be caused by any additional cold water pipe restrainingstructures or hardware. The lateral forces transferred through thespherical bearing are also low enough that they can be adequatelyaccommodated without the need for vertical restraint of the cold waterpipe.

Aspects of the present systems and methods described allow for verticalinsertion of the cold water pipe upwardly through the bottom of theplatform. This is accomplished by lifting the fully assembled cold waterpipe into position from below the platform. This facilitatessimultaneous construction of the platform and pipe as well as providingfor easy installation and removal of the cold water pipe formaintenance.

Referring to FIG. 3, cold water pipe 217 connects to the submergedportion 311 of spar platform 310 at cold water pipe connection 375. Insome embodiments, the cold water pipe connects using a dynamic bearingwith the bottom portion of the OTEC spar of FIG. 3.

In some embodiments, a cold water pipe connection is provided comprisinga pipe collar seated via a spherical surface to a movable detent. Themovable detent is coupled to the base of the spar platform.Incorporating the movable detent allows for vertical insertion andremoval of the cold water pipe into and from the cold water pipereceiving bay.

FIG. 13 illustrates an exemplary aspect wherein cold water pipeconnection 375 includes pipe receiving bay 776 comprising bay walls 777and detent housings 778. Receiving bay 776 further comprises receivingdiameter 780, which is defined by the length of the diameter between baywalls 777. In some embodiments, the receiving diameter is larger thanthe outer collar diameter 781 of cold water pipe 217.

Cold water pipe connection 375 and the lower portion of spar 311 caninclude structural reinforcement and supports to bear the weight anddynamic forces imposed on and transferred to spar 311 by the cold waterpipe 217 once suspended.

Referring to FIG. 14, cold water pipe connection 375 includes detenthousing 778 and movable detent 840, which is mechanically coupled to thedetent housing 778 to allow for movement of detent 840 from a firstposition to a second position. In a first position, movable detent 840is housed within detent housing 778 such that the detent 840 does notprotrude inwardly toward the center of the receiving bay 776 and remainsoutside of receiving diameter 780. In the first position, the top endportion 385 of cold water pipe 217 can be inserted into the pipereceiving bay 776 without interference from the moveable detent 840. Insome embodiments, movable detent 840 can be housed in a first positionsuch that no aspect of the movable detent 840 protrudes inwardly towardthe center of receiving bay 776 past the outer collar diameter 781. Insome embodiments, movable detent 840 in a first position does notinterfere with the vertical movement of the cold water pipe 217 throughreceiving bay 776.

In a second position, movable detent 840 extends beyond detent housing778 and protrudes inwardly toward the center of receiving bay 776. Inthe second position, movable detent 840 extends inwardly past the outercollar diameter 781. Movable detent 840 can be adjusted or moved from afirst position to a second position using hydraulic actuators, pneumaticactuators, mechanical actuators, electrical actuators,electro-mechanical actuators, or a combination of the above.

Movable detent 840 includes a partial spherical or arcuate bearingsurface 842. Arcuate bearing surface 842 is configured to provide adynamic bearing to cold water pipe bearing collar 848 when movabledetent 840 is in a second position.

Cold water pipe bearing collar 842 includes collar bearing surface 849.Arcuate bearing surface 842 and collar bearing surface 849 can becooperatively seated to provide a dynamic bearing to support thesuspended weight of cold water pipe 217. Additionally, arcuate bearingsurface 842 and collar bearing surface 849 are cooperatively seated toaccount for relative motion between the cold water pipe 217 and theplatform 310 without unseating the cold water pipe 217. Arcuate bearingsurface 842 and collar bearing surface 849 are cooperatively seated toprovide a dynamic seal so that relatively warm water cannot enter pipereceiving bay 776 and ultimately cold water intake 350 once the coldwater pipe 217 is connected to the platform 310 via cold water pipeconnection 375. Once cold water pipe 217 is suspended, cold water isdrawn through the cold water pipe via one or more cold water pumps andflows via one or more cold water passages or conduits to the condenserportion of a multi-stage OTEC power plant.

Arcuate bearing surface 842 and collar bearing surface 849 can betreated with a coating such as a Teflon coating to prevent galvanicinteraction between the two surfaces.

It will be appreciated that any combination of a dynamic bearing surfaceand a movable detent or pinion to connect the cold water pipe to thefloating platform are contemplated in the claims and the disclosureherein. For example, in some embodiments, the arcuate bearing surface ispositioned above the movable detent, the arcuate bearing surface can bepositioned to the side of the movable detent, or even below the movabledetent. In some embodiments, the movable detent can be integral to thebottom portion of the floating platform as described above. In otherembodiments the movable detent can be integral to the cold water pipe.

FIG. 15 illustrates an exemplary method of attaching a cold water pipeto a floating platform, and more specifically an OTEC floating platform.The method includes rigging guide lines and downhauls from the platformto the fully assembled cold water pipe. The cold water pipe is thenlowered below the platform and aligned to the proper position. The coldwater pipe is then raised into the pipe receiving bay, the movabledetents or pinions are extended and the pipe is seated on the arcuatebearing surface.

More specifically, guiding cables are attached 910 to the fullyassembled cold water pipe 217. In an exemplary embodiment, the coldwater pipe 217 can include one or more inflatable sleeves to providebuoyancy during construction, movement, and upending of the cold waterpipe. After the guide wires are attached 910 to the cold water pipe, theone or more inflatable sleeves can be deflated 915 so that the coldwater pipe is negatively buoyant. In an embodiment, the cold water pipecan also include a clump weight or other ballast system that can bepartially or completely filled with water or other ballast material toprovide negative buoyancy to the cold water pipe.

The cold water pipe is then lowered 920 to a position below the coldwater pipe connection 375 of the floating OTEC platform 310. Ballast canagain be adjusted. The guide wires are adjusted 925 to properly positionthe cold water pipe below the cold water pipe connection 375 andalignment can be checked and confirmed 930 via video, remote sensors andother means. The cold water pipe assembly is then raised 935 to aposition such that the cold water pipe bearing collar 848 is above themovable detents 840 of the cold water pipe connection assembly. Raisingthe cold water pipe into the cold water pipe connection can be doneusing the guide wires, inflatable sleeves, detachable balloons or acombination of the same.

After the cold water pipe is raised 935 into the cold water pipeconnection, the movable detents are extended 940 to provide a dynamicbearing surface for the cold water pipe. The cold water pipe is thenlowered by adjusting the guide wires, deflating the inflatable sleevesor detachable balloons, or by adjusting the clump weight or otherballast system. A combination of the same may also be used.

It will be appreciated that guide wires, inflation lines, ballast linesand the like should remain unobstructed from each other during movementof the cold water pipe. Moreover, the movement of the cold water pipeshould not interfere with the mooring system of the OTEC platform.

In a further aspect of the systems and methods described, a staticconnection can be made between the cold water pipe and the sparstructure. In such aspects, the dynamic forces between the pipe and sparcan be accounted for by varying the flexibility of the pipe near the topportion of the pipe. By allowing for movement of the lower and middleportions of the cold water pipe, the need for a dynamic pipe connectionis reduced or avoided entirely. Avoiding the need for a gimbaledconnection removes costly moving parts and simplifies fabrication ofboth the lower spar portion and the cold water pipe

Referring to FIG. 16, a cold water pipe 1651 is connected to the lowerportion of spar 1611 without the use of the above described dynamicbearings. FIG. 16 illustrates the cold water pipe connected to the lowerportion of the spar structure in both the displaced and non-displacedconfigurations. The upper portions of the cold water pipe 1651—that isthose portion at and adjacently below the point of connection and thelower portion of spar 1611—are stiffened to provide a relativelyinflexible top portion 1651A of the cold water pipe. Below theinflexible top portion 1651A, relatively flexible middle portion 1651Bis provided. Below the flexible middle portion 1651B is a moderatelyflexible lower portion 1651C, which can comprise the largest portion ofthe cold water pipe assembly. A clump weight or ballast system can besecured to the bottom or any other part of the moderately flexible lowerportion 1651C.

As illustrated, the flexible middle portion 1651B allows for deflectionof the lower portions of the cold water pipe away from the line ofsuspension of the cold water pipe. The amount of deflection can bebetween 0.25 degrees and 30 degrees, depending on the length anddiameter of the cold water pipe suspended from the spar 1011.

Referring to FIG. 17, the static cold water pipe—to —spar connection isdetailed. The lower portion of spar 1611 includes receiving bay 1713 forreceiving top portion 1651A of cold water pipe 1651. Receiving bay 1713include tapered portion 1714 and contact pads 1715. Upper portion 1651Aof cold water pipe 1651 includes collar 1755 with tapered collar surface1756 and lifting lugs 1775. Cold water pipe 1651 is connected to spar1611 by lifting and retention cables 1777, which are secured to the coldwater pipe at lifting lugs 1775. Cables 1777 are attached to mechanicalwinches 1779 housed in the lower portion of Spar 1611.

In an exemplary method of connecting the cold water pipe to the sparplatform, the fully fabricated cold water pipe is lowered to a pointjust below the spar platform. Lifting and retention cables 1777 areconnected to lifting lugs 1775 by remotely operated vehicles. Tension istaken up in the cables using the aforementioned mechanical wincheshoused in the lower portion of spar 1611. As the upper portion 1651A ofcold water pipe 1651 enters receiving bay 1713, it is guided into properposition by tapered portion 1714 until a secure connection is madebetween tapered collar surface 1756 and contact pads 1715. Upon properplacement and secure connection of the cold water pipe in the receivingbay, the cables 1777 are mechanically locked to prevent downwardmovement of the cold water pipe 1651. Because water is flowing on theinside of the cold water pipe and surround the outside of the pipe, apressure seal is not necessary at the interface between the cold waterpipe and the spar structure. In some implementations the seal betweenthe cold water pipe and the spar structure minimizes water passageacross the seal. The upward force exerted on the connecting pad can beimparted by the lifting cables, the buoyancy of the cold water pipe, ora combination of both.

It will be appreciated that the number of lifting cables 1777 andcorresponding lifting lugs 1775 is dependent on the size, weight andbuoyance of the cold water pipe 1651. In some aspects, cold water pipe1651 can be positively, neutrally, or negatively buoyant. The number oflifting cables 1777 and corresponding lifting lugs 1775 is alsodependent on any ballasting associated with the cold water pipe as wellas the weight and buoyancy of the clump weight attached to the coldwater pipe. In aspects of the systems and methods described, 2, 3, 4, 5,6, or more lifting and retention cables can be used.

In additional aspects of the systems and methods described, the liftinglugs 1775 can comprise pad eyes bolted directly to the top of the coldwater pipe using known fastening and connecting techniques. For example,barrel sockets, hex socket, coddler pins and the like can beincorporated into the staved top portion of the cold water pipe.

In other aspects, a lifting collar can be installed to the top portionof the cold water pipe, the lifting collar comprising collar connectingsurface 1756 and lifting lugs 1755. The lifting collar can be the sameor different material as the cold water pipe. The lifting collar, whenattached to the cold water pipe can increase the rigidity of the coldwater pipe more than the rigidity associated with the upper portion1651A. FIG. 18 is an illustration of a lifting collar 1775 mounted to astaved cold water pipe 1651. The lifting collar can be mechanically,chemically, or thermally bonded to the upper portion 1651A of the coldwater pipe. For example, the same bonding resin to connect individualstave members of the cold water pipe can be used to connect the liftingcollar to the cold water pipe.

Example

In some embodiments, the cold water pipe 217 is constructed non-uniformsections so that its upper region may be rigidly secured to the sparwhile allowing for ample flexibility of its lower region.

FIG. 24 shows an example cold water pipe 217 that is about 2,500 ftlong, has an inner diameter of 21 ft, and a varying outside diameter andis divided into different sections. As shown, the cold water pipe 217includes three different sections (e.g., an upper section 217 a, amiddle section 217 b, and a lower section 217 c). Each of these sections217 a-217 c has a unique geometry, function, and internal design. Thecold water pipe sections 217 a-217 c are formed of various materials,such as, for example, fiber reinforced plastic (FRP), syntactic foam,and stainless steel.

As shown in FIG. 25, the upper section 217 a has an upper portion (e.g.,a spar interface section) 851 and a lower portion 853. The sparinterface section 851 functions as a structural transition between aspar and the second section 217 b. As shown, the spar interface section851 is sloped for easy capture when being drawn up into the spar duringattachment of the cold water pipe 217, and acts as a guide and maximizesclearance (minimizing contact and possible damage) between the coldwater pipe 217 and the spar. The sloped design also helps duringdetachment the cold water pipe 217 from the platform spare by maximizingclearance and reducing (e.g., minimizing) the possibility of contact anddamage.

The spar interface section 851 includes an engagement interface to allowthe spar to retain the cold water pipe 217. The engagement featuresinclude mating plates 855 that have insertion holes 857 therein forretention by a corresponding engagement interface of the spar. Asdiscussed below, the mating plates 855 are arranged around the outersurface of the spar interface section 851 and are mounted so that theyevenly contact corresponding plates mounted within the engagementinterface of the platform spar. During attachment of the cold water pipe217 to the platform spar, engaging members (e.g., ball locks) within inthe spar platform are inserted into the insertion holes 857 in themating plates 855 to secure the cold water pipe 217 in position foroperation.

As shown in FIG. 26, the top of the cold water pipe 217 is constructedof a composite material (e.g., FRP) and has an inner stainless steelframe structure. The top edge of the upper section 217 a has a stainlesssteel mating ring 859 that provides circumferential strength to the coldwater pipe 217. The mating ring 859 also serves as a flat surface whenthe cold water pipe 217 is attached to the spar, however, the matingring 859 does not typically contact a flat mating surface of theplatform spar. The space between the mating ring 859 and the flat matingsurface of the spar is typically filled with gasket material to form aseal (e.g., watertight seal).

Face plates 861 are arranged around the inner and outer surfaces of thespar interface section 851 and are secured (e.g., welded) to the matingring 859. The face plates 861 around the inner surface of the sparinterface section 851 are connected (e.g., bolted) to the face plates861 arranged along the outer surface. Fastening the inner and outer faceplates 861 to one another adds strength to the connection joint betweenthe mating ring 859 and the FRP portion of the upper section 217 a. Theface plates 861 typically include countersunk holes so that the boltsconnecting the inner and outer face plates 861 do not extend outwardfrom the cold water pipe 217. The face plates 861 are made from metalmaterials. In some embodiments, face plates 861 are arranged around theinner and outer surfaces of the spar interface section 851.

Multiple tension beams 863 extend along nearly the entire verticaldistance of the upper section 217 a to provide tensile strength whileallowing slight angular flexure. The tension beams 863 are positionedwithin the FRP approximately between the inner and outer surfaces of theupper section 217 a and are bolted between the inner and outer faceplates 861. The tension beams 863 are made from metal materials.

In addition to fastening using bolts, the stainless steel components(e.g., the mating ring 859, the face plates 861, and the tension beams863) are secured to the FRP with adhesive.

Below the mating ring 859 and the face plates 861, the mating plates 855are arranged around the outer surface of the spar interface section. 851As shown in FIG. 27, similar to the outer face plates 861 welded to themating ring 859, the mating plates 855 are fastened (e.g., bolted) to aset of face plates 861 arranged around the inner surface of the sparinterface section 851. In some embodiments, that spar interface section851 includes mating plates evenly arranged around its outer surface.Each mating plate 855 is made of metal materials. When a correspondingball lock is inserted in the insertion hole 857, the mating plate 855can support a tensile load.

The mating plates 855 and the face plates 861 are bolted to one anotherand also to the tension beams 863 positioned within the FRP portionbetween the mating plate 855 and the face plate 861. Fastening themating plate 855 to the FRP portion, the tension beam 863, and the faceplate 861 strengthens the spar interface section 851 so that whenretained by a mating interface of the spar, the upper section 217 a cansupport the buoyant weight of the cold water pipe 217. Similar tosecuring the mating ring 859 and the upper face plates 861, the otherstainless steel components (e.g., the mating plates 855 and the faceplates 861) are secured to the FRP with adhesive.

Referring back to FIG. 25, the lower portion 853 of the upper section217 a includes a virtual hinge section 865 and a fixed interface 867 toengage the middle section 217 b. Due to its tapered design, the virtualhinge section 865 provides a structural transition and acts as a strainrelief between the rigid connection of the spar and the cold water pipe217 to allow for small angular motions of the cold water pipe 217. Dueto the flexibility of the middle section 217 b, as discussed below, theamount deflection in the virtual hinge 865 is typically smaller thanthat of the middle section 217 b. For example, the virtual hinge canallow for 1-2 degrees of motion.

As shown in FIG. 28, the fixed interface 867 near the lower end of theupper section 217 a provides a structural connection interface betweenthe upper and middle sections 217 a, 217 b. Similar to the upper end ofthe first section 217 a, face plates 861 are arranged around the innerand outer surfaces of the fixed interface 867 and fastened (e.g.,bolted) together. The inner and outer face plates 861 are fastenedtogether and also to a lower end of the tension beams 863 so the tensionbeams 863 can provide tensile strength to the upper section 217 a. Theface plates 861 can include countersunk holes so that the boltsconnecting the inner and outer face plates 861 do not extend outwardfrom the cold water pipe 217.

The fixed interface 867 includes recessed portions 869 between thetension beam 863 and the inner and outer face plates 861 to receivecorresponding tab features 871 of the middle section 217 b. In somecases, the recessed portions 869 are formed by removing (e.g., bymachining) portions of the FRP between the tension beam 863 and the faceplates 861.

FIG. 29 shows the middle section 217 b that includes multiple (e.g.,about 70) pipe-ring segments 873. Each pipe-ring segment 873 is acylinder made from multiple (e.g., about 18) staves 875. The staves 875are typically about 35 ft long so that they can fit within a standardISO 40-ft container. Each stave 875 is constructed of composite (e.g.,FRP) outer skin and a foam-filled interior, resulting in a strong,resilient structure.

As shown in FIGS. 30 and 31, staves 875 are designed to be joined alongtheir longitudinal edges 876 and end edges 878. The longitudinal edges876 include grooves 877 and the grooves 877 of one stave can be joinedto a tab 879 of an adjacent stave. The staves 875 include end grooves(e.g., “biscuit pockets”) 881 on both the top and bottom edges and aninsert (e.g., a “biscuit”) 883 is inserted into both grooves 881 andfastened to the staves 875 using bolts and adhesive. Alternatively, thebiscuit 883 can be formed as a fixed extension of the stave 875.

Once adjacent staves 875 are joined, resin adhesive is injected throughresin insertion channels 885 to bind the edges of the staves 875.Telltale groves formed in the base of the staves 875 allow a smallamount of the resin adhesive to flow out when the resin insertionchannel 885 is filled with resin. During assembly of the pipe-ringsegments 873, the staves 875 are typically staggered so that the ends ofadjacent staves are offset vertically from one another (e.g., offset by5 ft).

Referring back to FIG. 29, reinforcement bands 887 are applied (e.g.,continuously or at intervals) around the middle section 217 b tocircumferentially strengthen the middle section 217 b and the jointsbetween two adjacent pipe-ring segments 873. For example, the middlesection 217 b can be wrapped with FRP reinforcement bands 887 at 5 ftintervals. At the top and bottom ends of the middle section 217 a, thestaves 875 are trimmed evenly to join the adjacent upper and lowersections 217 a, 217 c. Alternatively, some of the staves 875 can bepremanufactured to shorter or longer lengths so additional trimmingalong the edges is unnecessary.

Referring back to FIG. 28, the top edge of the middle section 217 bincludes tab features 871 extending upwardly that are sized andconfigured for inserting into the fixed interface's recessed portions869. As shown, with the upper and middle sections 217 a, 217 b joined,bolts fasten the inner and outer face plates 861 of the upper portion217 a to the tab features 871 and, in some cases, also to the tensionbeams 863.

The lower section 217 c (e.g., the base) serves as a cold water inlet ofthe cold water pipe 217. As shown in FIG. 32, the lower section 217 cincludes a bell mouth 889, a ballast weight 891, and net structure 893that connects the ballast weight 891 to the bell mouth 889. The netstructure 893 is formed by multiple cables arranged around the bellmouth 889 spaced from one another to prevent large marine life and otherobjects from entering the bell mouth 889 and cold water pipe 217.

In addition to being a mounting location for the net structure 893, theballast weight 891 provides a downward force to help maintain the coldwater pipe 217 in an approximately vertical orientation. For cold waterpipes constructed as described herein ballast weights 891 are typicallyused.

Similar to the first section 217 a, the bell mouth 889 and clump weight891 are made of FRP and has stainless steel structural components. Thelower section 217 c is attached to the middle section 217 b using afixed interface joint similar to the fixed interface joint that is usedto connect the middle section 217 b to the first section 217 a (shown inFIG. 28).

Heat Exchange System

FIGS. 3, 3A and 19 and 20 illustrate an implementation of the presentsystems and methods described wherein a plurality of multi-stage heatexchangers 420 are arranged about the periphery of OTEC spar 410. Heatexchangers 420 can be evaporators or condensers used in an OTEC heatengine. The peripheral layout of heat exchanges can be utilized withevaporator portion 344 or condenser portion 348 of an OTEC sparplatform. The peripheral arrangement can support any number of heatexchangers (e.g., 1 heat exchanger, between 2 and 8 heat exchangers,8-16 heat exchanger, 16-32 heat exchangers, or 32 or more heatexchangers). One or more heat exchangers can be peripherally arranged ona single deck or on multiple decks (e.g., on 2, 3, 4, 5, or 6 or moredecks) of the OTEC spar 410. One or more heat exchangers can beperipherally offset between two or more decks such that no two heatexchangers are vertically aligned over one another. One or more heatexchangers can be peripherally arranged so that heat exchangers in onedeck are vertically aligned with heat exchanges on another adjacentdeck.

Individual heat exchangers 420 can comprise a multi-stage heat exchangesystem (e.g., a 2, 3, 4, 5, or 6 or more heat exchange system). In anembodiment, individual heat exchangers 420 can be a cabinet heatexchanger constructed to provide minimal pressure loss in the warm seawater flow, cold sea water flow, and working fluid flow through the heatexchanger.

Referring to FIG. 21 an embodiment of a cabinet heat exchanger 520includes multiple heat exchange stages, 521, 522, 523 and 524. In animplementation the stacked heat exchangers accommodate warm sea waterflowing down through the cabinet, from first evaporator stage 521, tosecond evaporator stage 522, to third evaporator stage 523 to fourthevaporator stage 524. In another embodiment of the stacked heat exchangecabinet, cold sea water flows up through the cabinet from firstcondenser stage 531, to second condenser stage 532, to third condenserstage 533, to fourth condenser stage 534. Working fluid flows throughworking fluid supply conduits 538 and working fluid discharge conduits539. In an embodiment, working fluid conduits 538 and 539 enter and exiteach heat exchanger stage horizontally as compared to the vertical flowof the warm sea water or cold sea water. The vertical multi-stage heatexchange design of cabinet heat exchanger 520 facilitates an integratedvessel (e.g., spar) and heat exchanger design, removes the requirementfor interconnecting piping between heat exchanger stages, and ensuresthat virtually all of the heat exchanger system pressure drop occursover the heat transfer surface.

In an aspect, the heat transfer surface can be optimized using surfaceshape, treatment and spacing. Material selection such as alloys ofaluminum offer superior economic performance over traditional titaniumbase designs. The heat transfer surface can comprise 1000 Series, 3000Series or 5000 Series Aluminum alloys. The heat transfer surface cancomprise titanium and titanium alloys.

It has been found that the multi-stage heat exchanger cabinet enablesthe maximum energy transfer to the working fluid from the sea waterwithin the relatively low available temperature differential of the OTECheat engine. The thermodynamic efficiency of any OTEC power plant is afunction of how close the temperature of the working fluid approachesthat of the sea water. The physics of the heat transfer dictate that thearea required to transfer the energy increases as the temperature of theworking fluid approaches that of the sea water. To offset the increasein surface area, increasing the velocity of the sea water can increasethe heat transfer coefficient. But this greatly increases the powerrequired for pumping, thereby increasing the parasitic electrical loadon the OTEC plant.

Referring to FIG. 22A, a conventional OTEC cycle wherein the workingfluid is boiled in a heat exchanger using warm surface sea water. Thefluid properties in this conventional Rankine cycle are constrained bythe boiling process that limits the leaving working fluid toapproximately 3° F. below the leaving warm seawater temperature. In asimilar fashion, the condensing side of the cycle is limited to being noclose than 2° F. higher than the leaving cold seawater temperature. Thetotal available temperature drop for the working fluid is approximately12° F. (between 68° F. and 56° F.).

It has been found that a cascading multi-stage OTEC cycle allows theworking fluid temperatures to more closely match that of the sea water.This increase in temperature differential increases the amount of workthat can be done by the turbines associated with the OTEC heat engine.

Referring to FIG. 22B, an aspect of a cascading multi-stage OTEC cycleuses multiple steps of boiling and condensing to expand the availableworking fluid temperature drop. Each step requires an independent heatexchanger, or a dedicated heat exchanger stage in the cabinet heatexchanger 520 of FIG. 5. The cascading multi-stage OTEC cycle of FIG. 6b allows for matching the output of the turbines with the expectedpumping loads for the sea water and working fluid. This highly optimizeddesign would require dedicated and customized turbines.

Referring to FIG. 22C, a hybrid yet still optimized cascading OTEC cycleis shown that facilitates the use of identical equipment (e.g.,turbines, generators, pumps) while retaining the thermodynamicefficiencies or optimization of the true cascade arrangement of FIG.22B. In the hybrid cascade cycle of FIG. 22C, the available temperaturedifferential for the working fluid ranges from about 18° F. to about 22°F. This narrow range allows the turbines in the heat engine to haveidentical performance specifications, thereby lowering construction andoperation costs.

System performance and power output is greatly increased using thehybrid cascade cycle in an OTEC power plant. Table A compares theperformance of the conventional cycle of FIG. 22A with that of thehybrid cascading cycle of FIG. 22C.

TABLE A Estimated Performance for 100 MW Net Output Four Stage HybridConventional Cycle Cascade Cycle Warm Sea Water Flow 4,800,000 GPM3,800,000 GPM Cold Sea Water Flow 3,520,000 GPM 2,280,000 GPM Gross HeatRate 163,000 BTU/kWH 110,500

BTU/kWh

Utilizing the four stage hybrid cascade heat exchange cycle reduces theamount of energy that needs to be transferred between the fluids. Thisin turn serves to reduce the amount of heat exchange surface that isrequired.

The performance of heat exchangers is affected by the availabletemperature difference between the fluids as well as the heat transfercoefficient at the surfaces of the heat exchanger. The heat transfercoefficient generally varies with the velocity of the fluid across theheat transfer surfaces. Higher fluid velocities require higher pumpingpower, thereby reducing the net efficiency of the plant. A hybridcascading multi-stage heat exchange system facilitates lower fluidvelocities and greater plant efficiencies. The stacked hybrid cascadeheat exchange design also facilitates lower pressure drops through theheat exchanger. And the vertical plant design facilitates lower pressuredrop across the whole system.

FIG. 22D illustrates the impact of heat exchanger pressure drop on thetotal OTEC plant generation to deliver 100 MW to a power grid.Minimizing pressure drop through the heat exchanger greatly enhances theOTEC power plant's performance. Pressure drop is reduced by providing anintegrated vessel or platform-heat exchanger system, wherein the seawater conduits form structural members of the vessel and allow for seawater flow from one heat exchanger stage to another in series. Anapproximate straight line sea water flow, with minimal changes indirection from intake into the vessel, through the pump, through theheat exchange cabinets and in turn through each heat exchange stage inseries, and ultimately discharging from the plant, allows for minimalpressure drop.

Example

Aspects of the present systems and methods described provide anintegrated multi-stage OTEC power plant that will produce electricityusing the temperature differential between the surface water and deepocean water in tropical and subtropical regions. Aspects eliminatetraditional piping runs for sea water by using the off-shore vessel's orplatform's structure as a conduit or flow passage. Alternatively, thewarm and cold sea water piping runs can use conduits or pipes ofsufficient size and strength to provide vertical or other structuralsupport to the vessel or platform. These integral sea water conduitsections or passages serve as structural members of the vessel, therebyreducing the requirements for additional steel. As part of the integralsea water passages, multi-stage cabinet heat exchangers provide multiplestages of working fluid evaporation without the need for external waternozzles or piping connections. The integrated multi-stage OTEC powerplant allows the warm and cold sea water to flow in their naturaldirections. The warm sea water flows downward through the vessel as itis cooled before being discharged into a cooler zone of the ocean. In asimilar fashion, the cold sea water from deep in the ocean flows upwardthrough the vessel as it is warmed before discharging into a warmer zoneof the ocean. This arrangement avoids the need for changes in sea waterflow direction and associated pressure losses. The arrangement alsoreduces the pumping energy required.

Multi-stage cabinet heat exchangers allow for the use of a hybridcascade OTEC cycle. These stacks of heat exchangers comprise multipleheat exchanger stages or sections that have sea water passing throughthem in series to boil or condense the working fluid as appropriate. Inthe evaporator section the warm sea water passes through the first stagewhere it boils off some of the working fluid as the sea water is cooled.The warm sea water then flows down the stack into the next heatexchanger stage and boils off additional working fluid at a slightlylower pressure and temperature. This occurs sequentially through theentire stack. Each stage or section of the cabinet heat exchangersupplies working fluid vapor to a dedicated turbine that generateselectrical power. Each of the evaporator stages has a correspondingcondenser stage at the exhaust of the turbine. The cold sea water passesthrough the condenser stacks in a reverse order to the evaporators.

Referring to FIG. 23, an exemplary multi-stage OTEC heat engine 710utilizing a hybrid cascading heat exchange cycles is provided. Warm seawater is pumped from a warm sea water intake (not shown) via warm waterpump 712, discharging from the pump at approximately 1,360,000 gpm andat a temperature of approximately 79° F. All or parts of the warm waterconduit from the warm water intake to the warm water pump, and from thewarm water pump to the stacked heat exchanger cabinet can form integralstructural members of the vessel.

From the warm water pump 712, the warm sea water then enters first stageevaporator 714 where it boils a first working fluid. The warm waterexits first stage evaporator 714 at a temperature of approximately 76.8°F. and flows down to the second stage evaporator 715.

The warm water enters second stage evaporator 715 at approximately 76.8°F. where it boils a second working fluid and exits the second stageevaporator 715 at a temperature of approximately 74.5°.

The warm water flows down to the third stage evaporator 716 from thesecond stage evaporator 715, entering at a temperature of approximately74.5° F., where it boils a third working fluid. The warm water exits thethird stage evaporator 716 at a temperature of approximately 72.3° F.

The warm water then flows from the third stage evaporator 716 down tothe fourth stage evaporator 717, entering at a temperature ofapproximately 72.3° F., where it boils a fourth working fluid. The warmwater exits the fourth stage evaporator 717 at a temperature ofapproximately 70.1° F. and then discharges from the vessel. Though notshown, the discharge can be directed to a thermal layer at an oceandepth of or approximately the same temperature as the dischargetemperature of the warm sea water. Alternately, the portion of the powerplant housing the multi-stage evaporator can be located at a depthwithin the structure so that the warm water is discharged to anappropriate ocean thermal layer. In aspects, the warm water conduit fromthe fourth stage evaporator to the warm water discharge of the vesselcan comprise structural members of the vessel.

Similarly, cold sea water is pumped from a cold sea water intake (notshown) via cold sea water pump 722, discharging from the pump atapproximately 855,003 gpm and at a temperature of approximately 40.0° F.The cold sea water is drawn from ocean depths of between approximately2700 and 4200 ft, or more. The cold water conduit carrying cold seawater from the cold water intake of the vessel to the cold water pump,and from the cold water pump to the first stage condenser can comprisein its entirety or in part structural members of the vessel.

From cold sea water pump 722, the cold sea water enters a first stagecondenser 724, where it condenses the fourth working fluid from thefourth stage boiler 717. The cold seawater exits the first stagecondenser at a temperature of approximately 43.5° F. and flows up to thesecond stage condenser 725.

The cold sea water enters the second stage condenser 725 atapproximately 43.5° F. where it condenses the third working fluid fromthird stage evaporator 716. The cold sea water exits the second stagecondenser 725 at a temperature approximately 46.9° F. and flows up tothe third stage condenser.

The cold sea water enters the third stage condenser 726 at a temperatureof approximately 46.9° F. where it condenses the second working fluidfrom second stage evaporator 715. The cold sea water exits the thirdstage condenser 726 at a temperature approximately 50.4° F.

The cold sea water then flows up from the third stage condenser 726 tothe fourth stage condenser 727, entering at a temperature ofapproximately 50.4° F. In the fourth stage condenser, the cold sea watercondenses the first working fluid from first stage evaporator 714. Thecold sea water then exits the fourth stage condenser at a temperature ofapproximately 54.0° F. and ultimately discharges from the vessel. Thecold sea water discharge can be directed to a thermal layer at an oceandepth of or approximately the same temperature as the dischargetemperature of the cold sea water. Alternately, the portion of the powerplant housing the multi-stage condenser can be located at a depth withinthe structure so that the cold sea water is discharged to an appropriateocean thermal layer.

The first working fluid enters the first stage evaporator 714 at atemperature of 56.7° F. where it is heated to a vapor with a temperatureof 74.7° F. The first working fluid then flows to first turbine 731 andthen to the fourth stage condenser 727 where the first working fluid iscondensed to a liquid with a temperature of approximately 56.5° F. Theliquid first working fluid is then pumped via first working fluid pump741 back to the first stage evaporator 714.

The second working fluid enters the second stage evaporator 715 at atemperature approximately 53.0° F. where it is heated to a vapor. Thesecond working fluid exits the second stage evaporator 715 at atemperature approximately 72.4° F. The second working fluid then flow toa second turbine 732 and then to the third stage condenser 726. Thesecond working fluid exits the third stage condenser at a temperatureapproximately 53.0° F. and flows to working fluid pump 742, which inturn pumps the second working fluid back to the second stage evaporator715.

The third working fluid enters the third stage evaporator 716 at atemperature approximately 49.5° F. where it will be heated to a vaporand exit the third stage evaporator 716 at a temperature ofapproximately 70.2° F. The third working fluid then flows to thirdturbine 733 and then to the second stage condenser 725 where the thirdworking fluid is condensed to a fluid at a temperature approximately49.5° F. The third working fluid exits the second stage condenser 725and is pumped back to the third stage evaporator 716 via third workingfluid pump 743.

The fourth working fluid enters the fourth stage evaporator 717 at atemperature of approximately 46.0° F. where it will be heated to avapor. The fourth working fluid exits the fourth stage evaporator 717 ata temperature approximately 68.0° F. and flow to a fourth turbine 734.The fourth working fluid exits fourth turbine 734 and flows to the firststage condenser 724 where it is condensed to a liquid with a temperatureapproximately 46.0° F. The fourth working fluid exits the first stagecondenser 724 and is pumped back to the fourth stage evaporator 717 viafourth working fluid pump 744.

The first turbine 731 and the fourth turbine 734 cooperatively drive afirst generator 751 and form first turbo-generator pair 761. Firstturbo-generator pair will produce approximately 25 MW of electric power.

The second turbine 732 and the third turbine 733 cooperatively drive asecond generator 752 and form second turbo-generator pair 762. Secondturbo-generator pair 762 will produce approximately 25 MW of electricpower.

The four stage hybrid cascade heat exchange cycle of FIG. 7 allows themaximum amount of energy to be extracted from the relatively lowtemperature differential between the warm sea water and the cold seawater. Moreover, all heat exchangers can directly supportturbo-generator pairs that produce electricity using the same componentturbines and generators.

It will be appreciated that multiple multi-stage hybrid cascading heatexchangers and turbo generator pairs can be incorporated into a vesselor platform design.

Example

An offshore OTEC spar platform includes four separate power modules,each generating about 25 MWe Net at the rated design condition. Eachpower module comprises four separate power cycles or cascadingthermodynamic stages that operate at different pressure and temperaturelevels and pick up heat from the sea water system in four differentstages. The four different stages operate in series. The approximatepressure and temperature levels of the four stages at the rated designconditions (Full Load—Summer Conditions) are:

Turbine inlet Condenser Pressure/Temp. Pressure/Temp. (Psia)/(° F.)(Psia)/(° F.) 1 Stage 137.9/74.7  100.2/56.5 2″ Stage 132.5/72.4 93.7/533′ Stage 127.3/70.2  87.6/49.5 4″ Stage 122.4/68  81.9/46

The working fluid is boiled in multiple evaporators by picking up heatfrom warm sea water (WSW). Saturated vapor is separated in a vaporseparator and led to an ammonia turbine by STD schedule, seamless carbonsteel pipe. The liquid condensed in the condenser is pumped back to theevaporator by 2×100% electric motor driven constant speed feed pumps.The turbines of cycle-1 and 4 drive a common electric generator.Similarly the turbines of cycle-2 and 3 drive another common generator.In an aspect there are two generators in each plant module and a totalof 8 in the 100 MWe plant. The feed to the evaporators is controlled byfeed control valves to maintain the level in the vapor separator. Thecondenser level is controlled by cycle fluid make up control valves. Thefeed pump minimum flow is ensured by recirculation lines led to thecondenser through control valves regulated by the flow meter on the feedline.

In operation the four (4) power cycles of the modules operateindependently. Any of the cycles can be shutdown without hamperingoperation of the other cycles if needed, for example in case of a faultor for maintenance. But that will reduce the net power generation of thepower module as a whole module.

Aspects of the present systems and methods described require largevolumes of seawater. There will be separate systems for handling coldand warm seawater, each with its pumping equipment, water ducts, piping,valves, heat exchangers, etc.

Seawater is more corrosive than fresh water and all materials that maycome in contact with it need to be selected carefully considering this.The materials of construction for the major components of the seawatersystems will be:

Large bore piping: Fiberglass Reinforced Plastic (FRP)

Large seawater ducts & chambers: Epoxy-coated carbon steel

Large bore valves: Rubber lined butterfly type

Pump impellers: Suitable bronze alloy

Unless controlled by suitable means, biological growths inside theseawater systems can cause significant loss of plant performance and cancause fouling of the heat transfer surfaces leading to lower outputsfrom the plant. This internal growth can also increase resistance towater flows causing greater pumping power requirements, lower systemflows, etc. and even complete blockages of flow paths in more severecases.

The Cold Sea Water (“CSW”) system using water drawn in from deep oceanshould have very little or no bio-fouling problems. Water in thosedepths does not receive much sunlight and lack oxygen, and so there arefewer living organisms in it. Some types of anaerobic bacteria may,however, be able to grow in it under some conditions. Shock chlorinationwill be used to combat bio-fouling.

The Warm Sea Water (“WSW”) system handling warm seawater from near thesurface will have to be protected from bio-fouling. It has been foundthat fouling rates are much lower in tropical open ocean waters suitablefor OTEC operations than in coastal waters. As a result, chemical agentscan be used to control bio-fouling in OTEC systems at very low dosesthat will be environmentally acceptable. Dosing of small amounts ofchlorine has proved to be very effective in combating bio-fouling inseawater. Dosages of chlorine at the rate of about 70 ppb for one hourper day, is quite effective in preventing growth of marine organisms.This dosage rate is only 1/20th of the environmentally safe levelstipulated by EPA. Other types of treatment (thermal shock, shockchlorination, other biocides, etc.) can be used from time to timein-between the regimes of the low dosage treatment to get rid ofchlorine-resistant organisms.

Necessary chlorine for dosing the seawater streams is generated on-boardthe plant ship by electrolysis of seawater. Electro-chlorination plantsof this type are available commercially and have been used successfullyto produce hypochlorite solution to be used for dosing. Theelectro-chlorination plant can operate continuously to fill-up storagetanks and contents of these tanks are used for the periodic dosingdescribed above.

All the seawater conduits avoid any dead pockets where sediments candeposit or organisms can settle to start a colony. Sluicing arrangementsare provided from the low points of the water ducts to blow out thedeposits that may get collected there. High points of the ducts andwater chambers are vented to allow trapped gases to escape.

The Cold Seawater (CSW) system will consist of a common deep waterintake for the plant ship, and water pumping/distribution systems, thecondensers with their associated water piping, and discharge ducts forreturning the water back to the sea. The cold water intake pipe extendsdown to a depth of more than 2700 ft, (e.g., between 2700 ft to 4200ft), where the sea water temperature is approximately a constant 40° F.Entrance to the pipe is protected by screens to stop large organismsfrom being sucked in to it. After entering the pipe, cold water flows uptowards the sea surface and is delivered to a cold well chamber near thebottom of the vessel or spar.

The CSW supply pumps, distribution ducts, condensers, etc. are locatedon the lowest level of the plant. The pumps take suction from the crossduct and send the cold water to the distribution duct system. 4×25% CSWsupply pumps are provided for each module. Each pump is independentlycircuited with inlet valves so that they can be isolated and opened upfor inspection, maintenance, etc. when required. The pumps are driven byhigh-efficiency electric motors.

The cold seawater flows through the condensers of the cycles in seriesand then the CSW effluent is discharged back to the sea. CSW flowsthrough the condenser heat exchangers of the four plant cycles in seriesin the required order. The condenser installations is arranged to allowthem to be isolated and opened up for cleaning and maintenance whenneeded.

The WSW system comprises underwater intake grills located below the seasurface, an intake plenum for conveying the incoming water to the pumps,water pumps, biocide dosing system to control fouling of the heattransfer surfaces, water straining system to prevent blockages bysuspended materials, the evaporators with their associated water piping,and discharge ducts for returning the water back to the sea.

Intake grills are provided in the outside wall of the plant modules todraw in warm water from near the sea surface. Face velocity at theintake grills is kept to less than 0.5 ft/sec. to minimize entrainmentof marine organisms. These grills also prevent entry of large floatingdebris and their clear openings are based on the maximum size of solidsthat can pass through the pumps and heat exchangers safely. Afterpassing through these grills, water enters the intake plenum locatedbehind the grills and is routed to the suctions of the WSW supply pumps.

The WSW pumps are located in two groups on opposite sides of the pumpfloor. Half of the pumps are located on each side with separate suctionconnections from the intake plenum for each group. This arrangementlimits the maximum flow rate through any portion of the intake plenum toabout 1/16th of the total flow and so reduces the friction losses in theintake system. Each of the pumps are provided with valves on inlet sidesso that they can be isolated and opened up for inspection, maintenance,etc. when required. The pumps are driven by high-efficiency electricmotors with variable frequency drives to match pump output to load.

It is necessary to control bio-fouling of the WSW system andparticularly its heat transfer surfaces, and suitable biocides will bedosed at the suction of the pumps for this.

The warm water stream may need to be strained to remove the largersuspended particles that can block the narrow passages in the heatexchangers. Large automatic filters or ‘Debris Filters’ can be used forthis if required. Suspended materials can be retained on screens andthen removed by backwashing. The backwashing effluents carrying thesuspended solids will be routed to the discharge stream of the plant tobe returned to the ocean. The exact requirements for this will bedecided during further development of the design after collection ofmore data regarding the seawater quality.

The strained warm seawater (WSW) is distributed to the evaporator heatexchangers. WSW flows through the evaporators of the four plant cyclesin series in the required order. WSW effluent from the last cycle isdischarged at a depth of approximately 175 feet or more below the seasurface. It then sinks slowly to a depth where temperature (andtherefore density) of the seawater will match that of the effluent.

Though embodiments herein have described multi-stage heat exchanger in afloating offshore vessel or platform, drawing cold water via acontinuous, offset staved cold water pipe, it will be appreciated thatother embodiments are within the scope of the systems and methodsdescribed. For example, the cold water pipe can be connected to a shorefacility. The continuous offset staved pipe can be used for other intakeor discharge pipes having significant length to diameter ratios. Theoffset staved construction can be incorporated into pipe sections foruse in traditional segmented pipe construction. The multi-stage heatexchanger and integrated flow passages can be incorporated into shorebased facilities including shore based OTEC facilities. Moreover, thewarm water can be warm fresh water, geo-thermally heated water, orindustrial discharge water (e.g., discharged cooling water from anuclear power plant or other industrial plant). The cold water can becold fresh water. The OTEC system and components described herein can beused for electrical energy production or in other fields of useincluding: salt water desalination: water purification; deep waterreclamation; aquaculture; the production of biomass or biofuels; andstill other industries.

All references mentioned herein are incorporated by reference in theirentirety. Other embodiments are within the scope of the followingclaims.

What is claimed is:
 1. An ocean thermal energy conversion plantcomprising: a vessel; and a cold water pipe attached to the vessel, thecold water pipe comprising: an interface section with an engagementportion in contact with the vessel and a virtual hinge extending fromthe engagement portion to a fixed interface; a middle section engagingthe fixed interface and suspended from the interface section; and anintake section suspended from the middle section.
 2. The ocean thermalenergy conversion plant of claim 1, wherein the virtual hinge is taperedfrom a first diameter adjacent the engagement portion to a smallersecond diameter adjacent the fixed interface.
 3. The ocean thermalenergy conversion plant of claim 1, wherein the engagement portion ofthe interface section is tapered from a first diameter adjacent thevirtual hinge to a smaller second diameter at the end of the interfacesection in contact with the vessel.
 4. The ocean thermal energyconversion plant of claim 1, wherein the virtual hinge is configured toprovide up to 2 degrees of deflection.
 5. The ocean thermal energyconversion plant of claim 1, wherein the cold water pipe is between2,000 and 3,000 feet long and has an inner diameter between 15 and 25feet.
 6. The ocean thermal energy conversion plant of claim 1, whereinthe engagement portion includes mating plates with insertion holes sizedto receive engaging members on the vessel.
 7. The ocean thermal energyconversion plant of claim 6, wherein the mating plates are arrangedaround the outer surface of the spar interface section.
 8. The oceanthermal energy conversion plant of claim 7, wherein the vessel comprisesreceiving plates aligned with mating plates.
 9. The ocean thermal energyconversion plant of claim 6, wherein the engaging members comprise balllocks within in the vessel, the ball locks inserted into the insertionholes in the mating plates to secure the cold water pipe in position foroperation.
 10. The ocean thermal energy conversion plant of claim 1,wherein the interface section comprises a composite material (e.g., FRP)and has an inner stainless steel frame structure.
 11. The ocean thermalenergy conversion plant of claim 10, wherein a top edge of the interfacesection has a stainless steel mating ring.
 12. The ocean thermal energyconversion plant of claim 11, wherein mating plates are arranged aroundthe inner and outer surfaces of the interface section and are secured(e.g., welded) to the mating ring.
 13. The ocean thermal energyconversion plant of claim 12, wherein the face plates around the innersurface of the interface section are connected (e.g., bolted) to theface plates arranged along the outer surface.
 14. The ocean thermalenergy conversion plant of claim 12, wherein the interface sectioncomprises multiple tension beams extending along more than half of theentire vertical distance of the interface section to provide tensilestrength while allowing slight angular flexure.
 15. The ocean thermalenergy conversion plant of claim 14, wherein the tension beams arepositioned approximately between the inner and outer surfaces of theinterface section and are bolted between the inner and outer faceplates.
 16. The ocean thermal energy conversion plant of claim 14,wherein the fixed interface also comprises face plates are arrangedaround the inner and outer surfaces of the fixed interface and fastened(e.g., bolted) together and a lower end of the tension beams.
 17. Theocean thermal energy conversion plant of claim 16, wherein the fixedinterface includes recessed portions between the tension beams and theinner and outer face plates to receive corresponding tab features of themiddle section of the cold water pipe.
 18. The ocean thermal energyconversion plant of claim 1, wherein the middle section that includesmultiple (e.g., between 50 and 90, more than 55, more than 60, more than65, more than 70, less than 85, less than 80, less than 75, less than70) pipe-ring segments.
 19. The ocean thermal energy conversion plant ofclaim 18, wherein each pipe-ring segment is a cylinder made frommultiple (e.g., about 18) staves.
 20. The ocean thermal energyconversion plant of claim 19, wherein each stave is constructed ofcomposite (e.g., FRP) outer skin and a foam-filled interior.
 21. Theocean thermal energy conversion plant of claim 18, comprisingreinforcement bands are applied (e.g., continuously or at intervals)around the middle section.
 22. The ocean thermal energy conversion plantof claim 21, wherein the middle section is wrapped with FRPreinforcement bands at 5 foot intervals.
 23. The ocean thermal energyconversion plant of claim 1, wherein the intake section includes a bellmouth, a ballast weight, and net structure that connects the ballastweight to the bell mouth.
 24. The ocean thermal energy conversion plantof claim 23, wherein the net structure comprises multiple cablesarranged around the bell mouth spaced from one another to prevent largemarine life and other objects from entering the bell mouth and coldwater pipe.
 25. The ocean thermal energy conversion plant of claim 23,wherein the bell mouth and the clump weight are made of FRP and havestainless steel structural components.
 26. A method of connectingsubmerged vertical pipe to a floating structure comprising: connectinglifting and retention cables to an upper portion of a cold water pipe,wherein the cold water pipe upper portion comprises a lifting collarhaving a tapered connecting surface; drawing the cold water pipe into aspar receiving bay using the lifting and retention cables, wherein thereceiving bay comprises a tapered surface for receiving the cold waterpipe upper portion and a contact pad; causing the tapered connectingsurface of cold water pipe to make a sealable contact with the contactpad of the receiving bay; and mechanically fixing the lifting cables tomaintain the sealable contact between the connecting surface and thecontact pad.
 27. A submerged pipe connection assembly comprising: aconnection structure comprising a lower portion having lifting devices,lifting cables, a first tapered connecting surface and a contact pad;and a vertical pipe comprising: a first longitudinal portion comprisinga lifting collar having a second tapered connecting surface and liftingeyes; a second longitudinal portion below the first portion, wherein thesecond portion is more flexible than the first portion.
 28. Thesubmerged pipe connection assembly of claim 27 further comprising: athird longitudinal portion below the second longitudinal portion andwherein the third portion is less flexible than the second portion. 29.The submerged pipe connection assembly of claim 27 wherein the secondtapered connecting surface is in contact with the contact pad of thefirst tapered connecting surface so as to form a watertight seal. 30.The submerged pipe connection assembly of claim 27 wherein the assemblyis part of an OTEC system.
 31. A submerged vertical pipe connectioncomprising: a floating structure having a vertical pipe receiving bay,wherein the receiving bay has a first diameter; a vertical pipe forinsertion into the pipe receiving bay, the vertical pipe having a seconddiameter smaller than the first diameter of the pipe receiving bay; abearing surface; and one or more detents operable with the bearingsurface, wherein the detents define a diameter that is different thanthe first or second diameter when in contact with the bearing surface.32. A method of connecting a submerged vertical pipe to a floatingplatform comprising: providing a floating structure having a verticalpipe receiving bay, wherein the pipe receiving bay has a first diameter;providing a vertical pipe having a top end portion that has a seconddiameter that is less than the first diameter; inserting the top endportion of the vertical pipe into the receiving bay; providing a bearingsurface for supporting the vertical pipe; extending one or more detentssuch that the one or more detents have a diameter that is different fromthe first or second diameters; and contacting the one or more detentswith the bearing surface to suspend the vertical pipe from the floatingstructure.
 33. A pipe comprising: an elongated tubular structure havingan outer surface, a top end and a bottom end, the tubular structurecomprising: a plurality of first and second stave segments, each stavesegment having a top portion and a bottom portion, wherein the topportion of the second stave segment is offset from the top portion ofthe first staved segment.
 34. The pipe of claim 33 wherein each stavesegment comprises polyvinyl chloride (PVC), chlorinated polyvinylchloride (CPVC), fiber reinforced plastic (FRP), reinforced polymermortar (RPMP), polypropylene (PP), polyethylene (PE), cross-linkedhigh-density polyethylene (PEX), polybutylene (PB), acrylonitrilebutadiene styrene (ABS); polyester, fiber reinforced polyester, nylonreinforced polyester, vinyl ester, fiber reinforced vinyl ester, nylonreinforced vinyl ester, concrete, ceramic, or a composite of one or morethereof.
 35. A method of forming a cold water pipe for use in an OTECpower plant, the method comprising: forming a plurality of first andsecond stave segments; and adhesively bonding alternating first andsecond stave segments such that the second stave segments are offsetfrom the first stave segments to form a continuous elongated tube.